I tried yesterday. I could get online easily, but no-one I sent an invite could apart from joebob.
I am assuming it is not a port/NAT problem as I had played in the morning with some people who could not login in the evening.
As I mentioned elseweher, there is no way to browse open games easily and the host has the option to eiterh reserve x amount of friends slots and leave the rest public.
Only way to play with a mixture of people on and off your list would be reserve some slots, and then in the lobby kick people who are not on your list, that you don't recognise from OcUK.
Easiest way will still be if all people you wish to play are on your list (why you can't do send an invite and specify a PSN tag manually, I don't know).
I have zapped non GTA owning (heathens!) people from my list so have a few slots free. I will definitely be playing online tonight from 7ish onwards (Just a s cool way to explore the city and mess around without messing up my SP game save more than anything).
Ideal scenario would be 16 of us in a map, break the law and just fend off the police as long as we can, did this yesterday briefly but a few people did not get it and kept killing me!!!
rp2000