If a pattern uses straights, I, too reach for my circs and knit as the pattern says.
I used straights for years, but discovered that I prefer using circs for everything. I haven't used a straight needle in a couple of years and gave away all my long ones to my son's girlfriend. Plus I never lose the 'other' needle in the couch or forget to take it with me. DPN's, however, are a different story. :teehee:
You don't have to switch by any means, and many people still like their straights. It's just a personal preference.