Personally, straight but I'm under the impression that anyone has to POTENTIAL for any sexual orientation. Been my experience that most people tend to lean toward the gender whose emotional norms either interests them more, or they find easier to mesh with. I like girls so much better simply because girls are more fun to try to figure out.
As far as physical appearance goes, you can condition yourself to find anything attractive with enough work. I pulled a psych experiment on myself to test this theory and it worked. For a short time I managed to convince myself I was attracted to guys for a short time, and it showed up in my fantasies. Granted because my default preference is girls it took significantly less time to reverse it, but (at least with me) it is possible. If your wondering why if that's the case I don't say I'm bi, it's simply because after I "deprogrammed" myself I was no longer attracted to guys. Weird I know, but it's amazing what you can do to influence your own interests. Never underestimate the power of suggestion...
/end rant_mode
I hope this isn't to far enough topic to be considered spam...