Online seems pretty underwhelming so far...
1) Huge load times
2) Lots of griefers just hanging out at the airport
3) Fair few times it just hangs or you get disconnected without knowing and continue to play the game despite not actually being on the server.
It has its moments though, and is heaps better playing with a crew. (p.s. Apologies to the guy I killed on ps3, I haven't seen a crew symbol for so long that I forgot what it meant. Name started with a T).
To avoid hassles, ive always avoided buying the eclipse towers apartments (being the most expensive, it's what everyone else buys, and there's always someone hanging out there making life difficult)
I usually go elsewhere for air transport, there's the roof of the hospital near the strippers, the helicopter scenic flights between the airport and the marina, and the other chopper that spawns at the end of the submarine construction dock halfway between the airport and simeons garage. Further afield there's the desert airfield, Trevor's airfield, the police station north of the airbase, the airbase itself, and the FIB rooftop.
Load times aren't too bad on ps3 anymore, though that could be because most are on next gen.