Why should I put up with the inconvenience of lugging around a DSLR?
They look cool, but is there more substance to it?
It depends on what you wish to do. If all you need is to take a few shots of your friends and family in various life situations, a P&S will serve you well. However, if you wish to have total control over your photos, and are interested in the composition, lighting, and ultimate quality of your shots, a DSLR will serve you better.
I personally don't think of my DSLR as "cool". It is a tool that lets me accomplish something that has value to me. With a DSLR, you don't just get higher megapixels and a heavier camera. You get more features that give you the power and control you need to fine-tune your shots, and capture the moments that you find meaningful in the best way possible.
Here are some of the benefits of a decent DSLR over a P&S:
A DSLR is an amazing device, and if you have the need for any of the above, it can serve you well. It is certainly not an ad-hoc camera that will let you quickly and cheaply capture those zillions of friend and family moments that happen every day...but it will let you capture those fantastic moments that you pass by on rarer occasions in perfect clarity and quality.
They aren't better per se; They just tend to allow greater artistic control over the result. They're useless for just keeping in your pocket for that surprise sunset, or random performance in town.
I'd advocate having the right camera for you. In my case, I'm quite indecisive so that's a DSLR, film SLR, and a digital compact.
To answer my own question, my reasons:
The above is not true for all P&S cameras. Please comment on notable exceptions.
If you're not feeling the limitations of your point-and-shoot camera, then you probably don't need a DSLR. (Not least because, if you're happy with the P&S, you'll probably leave the DSLR at home when you go out!)
DSLRs have loads of extra capabilities, but will you actually use them?
I solved this dilemma for myself by taking a weekend photography course with my P&S camera (it has a fairly limited manual mode, which was enough). I learned a lot, took lots of photos that were much better than usual, and I got a really clear idea of what I personally could do with a DSLR. And then I bought my first Canon about a month later...
The "better" camera is the one that best fulfills your needs.
If you want to always carry the camera without being burdened by its weight (and the weight of extra lenses) and be able to take a picture quickly and unnoticed, and IQ is not of paramount importance, then a P&S is better.
If you want to spend time thinking about the perfect shot, set up your tripod, put on filters, figure out individual settings for shutter speed, aperture, iso, etc. and post process the RAW file in an image editing software to create a piece of art, then the SLR is better.
Basically, a larger and better sensor and the ability to use a variety of lenses, from cheap and crappy to astonishingly expensive and good - which don't always go together. :)
The Micro 4/3 cameras are somewhat of a middle ground.
Speed has been mentioned. Here is an example of speeds of two P&S and two DSLR from roughly the same price level.
Canon S100 is a pretty nice P&S pocket camera, Samsung EX2F a slightly bigger P&S with features left out from many small pocket cameras, Nikon D5100 a DSLR with optical viewfinder and Sony A37 a DSLR with electronic viewfinder.
Shutter lag is the time camera needs to take the photo from the moment the shutter release is pressed. There is variations in how to do it. Shortest lag usually happens when camera has already focused and only needs to take the shot, which happens when you have the shutter release pressed halfway and focus has locked:
Shutter lag after half-pressing and holding the button:
Canon PowerShot S100 - Samsung EX2F - Nikon D5100 - Sony SLT-A37 0,071 second - 0,130 sec - 0,114 sec - 0,057 sec
More typical shutter lag for the idea of "point and shoot" would happen when we simply point and press the shutter release down, and the camera takes its time to focus and exposure metering:
Shutter lag after fully pressing the button (with center area autofocus):
Canon PowerShot S100 - Samsung EX2F - Nikon D5100 - Sony SLT-A37 0,571 second - 0,380 sec - 0,273 sec - 0,109 sec
Next, you have your camera at hand, but power turned off, and you see something you want to take a photo of. Forgetting about the time needed to pull your camera out from pocket or bag, here is the time needed between turning power On and having the first photo captured:
Canon PowerShot S100 - Samsung EX2F - Nikon D5100 - Sony SLT-A37 2,4 seconds - ~1,7 sec - ~0,5 sec - ~0,9 sec
Here it shows how Nikon D5100 as a true DSLR with optical viewfinder beats them all, and the pocket cameras perform typically slow on power-up. Anyhow, when you know you are going to take a photo, and your target is relatively still, you should let the camera focus itself by half-pressing the shutter release button and wait for your moment. Then you'll have almost the same shutter lag with any one of these four cameras. You will get the hand-shake captured, or whatever it was you waited to happen.
Also remember, Point&Shoot is a photographying style, not really a camera type. You can use an expensive DSLR as a P&S on full Auto mode, and similarly you can go using all the possible manual controls there is on those small pocket cameras. Differences are found in weight, image quality and possibilities. With a DSLR you can do so much more than just point and shoot.
Adding two sample shots. One representing point-n-shoots and one representing entry level DSLRs. Both photos were taken with settings ISO 200 and f/8.0 and lens at maximum zoomed-in. Shutter speeds varied a bit due to them being different cameras, but also roughly the same anyway. Both cameras can take RAW photos, so that was used.
^^ Olympus SP-550 ultrazoom (18x zoom was "ultra" when released in 2008) - 35 mm equivalent focal length: 500 mm
^^ Sony SLT A37 (released in 2012) with Sigma DG 70-300 mm zoom lens. - 35 mm equivalent focal length: 450 mm
Difference in detail is most prominent in the grey lichen just above the small piece of concrete.
Difference in noise is obvious in the yellow area. The small size of a sensor in a compact camera is prone to high level of noise, in this case already at ISO 200. The Olympus used here has about the smallest sensor there is in any compact. Sony's sensor is of the typical APS-C size. (sensor size vs. image quality)
Image quality is a combination of camera and lens quality (image quality). This comparison here is in fact meaningless, because - the Olympus has only 7 megapixel sensor while the Sony has a 16 megapixel sensor - Olympus is a 5 year old design and not in production anymore, while Sony is almost brand new - Olympus (when purchased) was in the better department of ultrazoom compact cameras, while Sony+Sigma are of the cheapest entry level and still cost twice the price of that Olympus. (No sense in comparison?)