There are two main reasons I am considering a dslr:
1-much better high ISO performance than I'm getting with my compact
digital cameras.
The much larger sensors in the DSLR cameras yield better high ISO results. This is one case where size really does make a difference.
2-faster and more accurate auto focusing. I'm really interested in
developing my skills at photographing birds in flight. With regards
to this, I want predictive autofocus.
The thing I found most useful for shooting birds in flight (BIFs) was the seeming less lack of shudder-lag. When you fully depress the shutter release button the picture is taken, there is no perceptible shudder-lag. The other thing I discovered is that the lens can have a big impact on the time to focus, possibly even more influence than the camera. But as you move up the model lineup you get more choices for how the camera focuses, and I generally believe that more choices are a good thing.
This individual shoots a lot of BIFs and uses a D40, most of the time, and displays some beautiful results; take a look at some of his threads,
http://forums.dpreview.com/forums/postersprofile.asp?poster=hjivijiehdig . I am supplying this as proof that BIFs can be successfully photographed even with an entry level camera.
I also enjoy photographing city and landscapes and taking natural
light photos of my grandchildren. So the thought of a f2.8 makes me
drool. If I think about my shooting style during the past years, I
love a long zoom.
F/2.8, or faster, lenses with few exceptions are pricey. The Super-Telephoto lenses are all now AF-S, but 300mm F/4.0 costs more than $1100, and the F/2.8 runs right around $4500; somewhat explaining the popularity of the much slower 70-300mm F/4.5-5.6 that can be purchased for less than $500.
For Grandkids something like the new Nikon 24-70mm F/2.8 might be perfect, but be prepared to pay around $1700; there is also the 17-55mm at around $1200 that is also a F/2.8 lens.
The bargain in fast lenses is the 50mm F/1.8 at around $115, which both fast and sharp, but it won’t AF on the D40/D60 cameras. There is also the 50mm F/1.4 at about 3X the cost, but again it is not an AF-S lens.
Many opine that manufacturer's are doing this on purpose, to drive
more people into the dslr market. Well, here I am.
I don't think that is the reason, I believe the reason is that even with today's advanced technology you can only do so much with the small sensors found in most of the digital cameras.
The thought of lugging around a heavy, bulky DSLR and lenses makes me
pause to think if I'm going in the right direction. Then I recall the
feel and responsiveness of a slr in my hands and the juices start
flowing.
The D80 weighs 1 pound 5 ounces, while the D60 weighs 1 pound 1 ounce; a difference of four ounces – the same as a stick of butter. The D80 is slightly bigger (WxHxD; 5.2x4.1x3.0 vs. 5.0x3.7x2.5) being two-tenths of an inch wider, four-tenths of an inch higher, and half an inch deeper. Not a lot of difference to be sure, but enough to make the two cameras feel different when you hold them. For some people the D40/D60 feels small in their hands (the Canon Rebels feel even more cramped). By comparison the D300 weighs 1 pound 13 ounces and is 5.8x3.5x2.9. Personally I don’t think a few ounces one way or the other are going to make a whole lot of difference, especially when you mount a fast lens (the 24-700 f/2.8 is only three-tenths of an ounce shy of weighing 2 pounds), but how the camera feels when you hold it may determine how much you use your camera. Ergonomics really comes into play with whether you will enjoy using your DSLR. I think the ergonomics of the Nikon are better than the ergonomics of the respective Canons, YMMV.
--
Brooks
http://bmiddleton.smugmug.com/ 
