My Mach III tore the crap out of my face, so for me that's the major benefit of a straight. But there's also the cost issue. Now I don't have to buy $3 blades that make my life miserable...
I used to dread shaving; since I'm not a morning person, that was one less reason to get out of bed. Now shaving is a pleasure, and I look forward to it. A good shave puts me in a good mood all day.
And then there's the manliness factor... :D
Josh