Tried account switching to use some DLC for some of the Japanese games I have and check out the Soul Sacrifice demo. You can now skip the stupid intro video (just power the system off/on), so it cuts down on a lot of time, but it was a pain in the ass switching back to my U.S. account- I knew the system would change the icon order, but some game icons were deleted entirely. (The save data for them was not) Also had to re-enter all my billing information.
It was just annoying enough that I doubt I'm going to be doing this very often.
Wait do you have to go thru the process if you have a different MC with the different region/goods?

One account per memory card now, so I had to do a factory restore and use the card with my J-account to access the DLC.
I think I'm just gonna switch back to the J-account this weekend, run through the DLC for Senran Kagura (

, uguu, etc.) and switch back. Nobody plays that game online anyway.
Wanted to use DLC for One Piece Kaizoku Musou 2 (which is SO GOOD on Vita- what the fuck is up with no English release?), but they just had some outfits and a throwaway challenge mission so I'll probably just stick to playing that on my U.S. account too.
Assuming you can use a 3G connection to setup PSN accounts, that's about the only reason I can think of where having a 3G Vita would have been useful.

I play my Vita a lot at work during downtime and don't have a wireless network to use for it, so account switching is a bigger deal for me since I'm locked into using whichever account it's set to if I'm not at home.