I agree with all here about the dominance of .com. BUT, for the first time I've added a .net and a .us to my portfolio of more than 50 names because they were just too cheap and too DOMINANT to pass up. For example, my flagship site, My Merry Christmas.com, has been up and active since 1999 and I've slowly added several related sites over the years. I just picked up XmasEve.us because...well, someday I should be able to make something of it and it will be valuable. It's a .com world but I think down the road that could change for the right names.
If I am going to reg something it has to be .com and then keywords. However I have a few .info domains simply because for $1.79 I can't resist picking some up every now and then.
Keywords and the way it sounds when you say it (always keep word of mouth in mind). Does it do what it says on the tin?