That's a nice list of features - thanks for the heads-up!
I particularly like (a) the easy way of running the CFW along with the standard firmware, and (b) the UMD backup feature for transfering existing UMD titles onto a PSPgo.
The UMD backup tool is something that Sony themselves should be encouraging IMO. They really missed the boat and screwed over PSP GO owners by not allowing them to get any of the games they paid for in UMD format. Even something as simple as posting off a UMD copy of a game and Sony send you a code to download a copy for the GO would really have helped the device. Being restricted to the limited and often overpriced PSN content has killed the GO. I'm sure there would be a way to create a backup of a UMD which also requires PSN account verification (like what happens when you download any game off the PSN) which will ensure it is only you who can play that copy and thus calm down and fears of piracy and people sharing backups.
People who only own a PSP Go are still of course left in the dark here which is crazy. When you are not even giving the option to pay, it comes down to a situation where you either don't get games which are available for every other model of PSP other than the most expensive one you bought, or are forced into piracy. Sony should have tried to expand the ways people can legally obtain games instead of leaving them with that conundrum.
Firmware 6.37 fixed the kernel exploit that the custom firmware I linked to uses, so if you've upgraded, you are stuck with what you have sadly.
Like others here, I don't encourage piracy at all and continue to buy minis and games from the PSN store. But the custom firmware really has made my Go the device it had the potential to be. I used to have the situation where it was carry around my bulky old 1st gen PSP, or make do without any of my UMD games. The pro firmware enabled me to have access to those (and my old Psone games!) on the go, and without resorting to downloading illegal copies of them.