Yeah, I guess there's really no point in buying straight needles since you can basically do anything on a circular. I just think straight needles look so much cooler (lame, I know!) so it's hard to resist the temptation to buy them. And they're at least half the price of circulars so sometimes I just buy those if the project I want to work on is knit flat. I also can't stand the cable in the circs. Maybe it's just the set I have (I got a set of Boye needles at Michael's), but the cable is stiff and plasticky and I feel like it kept getting in the way and it was extremely annoying. But it's also extremely annoying when I have a set of straights 7s and I come across a project I really want to try that uses a circular 7! So either way, I can't win!
I think I'll just go ahead and buy a 29" circular in a size 8. I watched the magic loop video on this site, and it seems pretty easy to do... I hope!