^This being an advantage of the Go over any other UMD-based model, and if the idea of playing a game on your television, pausing it, and then undocking your system to continue to play anywhere appeals to you (as it does me) then this is an advantage that cannot be overstated, especially at this price.
Easy-to-install CFW means it's easy to get all your retro favorites emulated, up to and including Neo Geo, CPS2 and near-perfect PSX compatibility (and even a small handful of N64 games run well!). CFW also lets you run backup copies of any UMDs you legally own, giving you the option to play the many disc-based games that were never made available on PSN.
It's also the only PSP that has a generous 16 gigs of storage built-in, and though Sony M2 cards are harder to find than Memory Stick Pro Duos, you can grab an extra 4 gigs at most Toys R Us stores right now on clearance for under 4 bucks.
A really, really underrated handheld system. I think you can find them used at GameStop for $50 as well.