I use Shift+Command+4 all the time to take screenshots on my Mac.
What I found out recently is that if you press the space bar after Shift+Command+4 then you can capture an entire window or pull down menu, without having to try to manually select its area without cutting off any pixels or including any extra.
Strangely, this doesn't seem to be mentioned in the Mac OS X Leopard Pocket Guide.
I use Techsmith Snagit on Windows and it has a similar option, but I like the Mac keyboard shortcut since it's always available without having to start another program. (I could leave Snagit running, but I prefer to not to have too much stuff running all the time.)