I recently bought a Canon 50mm f1.8 for my Canon 1000d. But, I find that the images are not as sharp as those I saw in the reviews or any other images taken using other cameras like the 550d and above. I shot in Raw as well as JPEG L ("fine" quality).
Does the lens produce different quality images depending on the camera used?
To an extent, yes. There are several ways in which the camera body can affect sharpness and image quality in general:
If your camera's autofocus is inaccurate, your subject might just be slightly out of focus, causing a loss of focus. The 550d has a cross-type center AF point which can focus more accurately with lenses faster than f/2.8; as far as I can tell, the 1000d lacks this.
The 550d is an 18 megapixel camera, almost twice the 10.1 megapixels you have. This means it (theoretically) can resolve about 34% smaller details than the 1000d. Generally, primes are sharp, so the limiting factor may in fact be the camera. Sometimes, the camera can out-resolve the lens, so a higher megapixel camera won't have as much of an effect on image sharpness.
High-ISO noise and noise reduction can also destroy a lot of detail. The 550d has an ISO range of 100-6400, compared to the 1000d's 100-1600. At the same ISO, I would expect that the 550d has much lower noise, meaning less detail-destroying noise reduction needs to be applied to the image.
Another benefit of having a camera capable of high ISOs is the ability to increase shutter speed. The 1000d may be able to produce a reasonably low-noise picture at ISO 1600, while you have to shoot at ISO 800 or ISO 400 to produce similar results. This means you'll have to decrease shutter speed to compensate if you want to keep aperture the same. Slower shutter speed = more motion blur, either by camera shake or from subject motion. A tripod can help you avoid camera shake, but won't keep your subject steady.
Keep in mind that lenses are generally sharpest when stopped down a bit — Wide open, some of the light has to bend at hard angles; stopped too far down, and you hit the diffraction limit. It appears that your lens is sharpest at about f/4.5. Also, a lot of the example images you find in reviews are shot outside, under daylight. A hard light source like the sun will give you sharp shadows and lots of contrast; this makes for a sharper-looking image.
DXO does lens tests on most camera bodies and offers different scores for each.
http://www.dxomark.com/Lenses/Canon/EF50mm-f-1-8-II-mounted-on-Canon-EOS-400D__184
Your 1000D is basically a 400D which gets a 13 compared to the 25 on the canon mark 3.
However, prime lenses are excellent performance wise....99% of the problem is the shooter if it's a prime lens.
