I personally don't like the fact that they completely removed the UMD slot from the PSP Go. I love the idea of downloading games and demos and new stuff from PSN all the time; I think it's a really great use of the PSP's Internet/Wi-Fi capabilities, and it's a great market too. But personally, I'd like to keep a true, physical copy of games I really value and hold dear. For example, I'll probably be able to easily download the upcoming MGS: Peace Walker, but I wanna keep that because I love the MGS series and have already buitl up quite the collection of both games but also books/memorabilia.
That's what it takes away from: collecting. There's a difference between saying, "look at all these PSP classics that I have in this ornate bookshelf" and saying "look at all the beautiful EBOOT.PBP files I have on my PSP's memstick".