I'm considering uploading some of my photos to a stock photo website as a way of getting a few $$$ back from what's essentially been a hobby for me.
Is this a sensible step, or am I likely doomed to disappointment and failure with this approach?
To answer your question, no, stock photos are not a viable source of income. You can make money off of it, just like some people who are able to write iPhone applications are able to make huge paydays; but in general the market is saturated, and unless you produce something that stands out amongst all the cruft, you won't be making much.
Think of it in terms of economics.
Supply and Demand.
Professional looking images required (in no particular order):
And back in the day, all three were fairly hard to come by. Camera equipment was expensive (especially digital), you hard to find someone willing to teach you the ropes, and it took a long time to learn. Now a days:
As such, the barrier to entry to producing quality images has been lifted nearly completely. With that, more and more people are able to produce nice images. One could say that stock photographs have become a commodity; there is no short supply of quality looking images.
Since the supply is very saturated, that drives the price down (while demand for stock photos has increased, it hasn't been to the scale as supply). Anyone with a digital camera and an internet connection can produce stock photos.
As Nick pointed out that as long as it doesn't cost you anything to submit your photos, you have nothing to lose.
This is outside your question, but if you want to make money off your photography, you're going to want to be creative and see what areas are underserved and target them. Assuming you are in the US, how about getting into real-estate photography--there is a huge glut of houses on the market and (at least when I was looking to buy a house) most have crap photos taken by real-estate agents. Another area, not for money necessarily--is to team up with animal shelters and do photos of the pets for adoption. Most shelters dont spend any time taking nice images, so volunteering your time will
Every photographer has a chance to make money with stock, but it depends on many factors. Read this article, which I wrote specifically on this subject, you will find a detailed answer to your question there: Getting Rich with Stock Photography Part 1: Dream or Reality?
If you want to try yourself in stock photography, you need to be prepared to work hard. Apart from taking photos, you will need to do much more work, such as: thoroughly check the quality of every photo, post process it as necessary, add key words, upload to agencies as well as watching trends, constantly work on developing your skills and so on.
Stock photography, like any other kind of paying work in photography, has its own requirements and demands, and is usually quite separate from the kind of work you'd do as a hobby.
In other words, it's a job. Like a lot of jobs in photography, it's a job with a huge amount of competition, and the rewards are distinctly uneven and unpredictable.
Perhaps a topic for another question, but if you have a day job that satisfies, and want to make a bit of money back from the photography you enjoy, think about selling prints or exhibiting. If you want to work as a professional photographer, there are much better fields to get into than stock photography (especially microstock sites).
For the most part, no.
There are a decent number of photographers out there that make money with stock photos, but there are many many more who never really make enough to justify the time put into it.
That being said, if you're willing to spend the time, there is money to be made. If you decide to give it a try, take a look at these ideas to keep in mind for stock photos.