The PSP offers the ability to watch movies in extremely clear detail (for a screen so small, mind) so why not take advantage of it especially if the UMD movies are on sale? For someone who travels a lot like me, I like the fact that I can pack JUST my very portable PSP and have the choice to either play games, watch movies, listen to music, or all of the above.
That said, I recently picked up Metropolis for $5 myself in the bargain bin at Fry's Electronics and Hero and The Crow for a bit more apiece at... someplace else.
I'm currently looking to acquire Gone in 60 Seconds without having to pay full price (or even half price) for it.
@ lurknomore: I honestly think that the price point will stick to $5 being the cheapest for a while longer (major major sales dates nonwithstanding) because while UMD movies are on the unpopular side, there are enough people who collect the UMDs which keeps the price from dropping to sub-clearance levels (unless the movie in question is a B-grade or lower title). That, and Sony-branded things just... don't tend to go sub-clearance unless they are wildly unpopular or have been known to have manufacturing defects or are simply completely defunct. Just my two cents.