The question of which one is better between Canon and Nikon has been going on and will always be going on for years and years. My opinion and it is ONLY that...my opinion... is:
I have owned many Canon cameras and camcorders and have been very happy with all. I just bought a 40D in January of 2008 because I had many Canon lenses. I also bought a Sony a200 as a daily carry camera. I have enjoyed the Sony so much I sold all my Canon equipment and bought a Sony a700 and like it better than the 40D. I have also used a Nikon d40, d40x and d60. They were nice and worked well...but I like my Sony. I have many friends that are photographers that swear by Canon or Nikon and wouldn't touch any thing except Canon or Nikon and argue all the time about which one is better.
So it comes down to this...If you do not have any money invested in lenses as of yet you can go either way. The Canon 40D has some great features as does the Nikon D90. If I were to look at specs: The Nikon D90 has many more features. The Canon 40D has faster frame rate and stronger construction.
So the Nikon would be the better choice.
To help you decide I would recommend that you go to your nearest BestBuy and spend a little time with both cameras at the demo stand. See which one feels right in YOUR hand...after all...it's going to spend a lot of time there. Just know that you can't go wrong with either one....

Both are good camcorders. Both have 60gb drives and both have Carl Zeiss Vario-Tessar lens. But the DCR-SR47 is a 60x Optical and the DCR-SR85 is only a 25x Optical. Shooting any sports you will be happier with the 60x Optical.

There could be a few things causing this before it's labeled broken. First make sure there is no finger prints or smudges on the lens glass. Next check the owners manual about auto focus points. This camera uses Multi-points AF, Center and Face detect. Check to see that you are using the right one for what you are shooting. The camera could be in face detect mode and there is no face to detect or the Multi-point and Center may be slightly off so what YOU think you are focusing on may not be what the CAMERA is focusing on.
If none of these are amiss then I suggest taking it to your nearest BestBuy and have the Geek Squad take a look.

The run down:
XSi has 12.2 megapixel (More data in image=more room to crop and bigger prints), 3.5 FPS (Frames Per Seconds of continuous shooting), 3” LCD Screen (Bigger and easier to see), 9 point auto focus (More points mean better coverage of viewing area for quicker focus) and Large internal memory buffer so photos are written quicker and camera is ready for next picture.
The XS has 10.1 megapixel (Less cropping area), 3 FPS, 2.5” Screen and 7 auto Focus Area.

The Xsi is much more camera for not very much more price.