If your chosen Guild Wars 2 server is full, you'll be offered the chance to play with that character anyway, thanks to overflow servers.
ArenaNet's Martin Kerstein wrote an explanation of the system on the Guild Wars 2 Guru forums.
"Let me explain what an overflow server is and what it does. It is a technology we also use as our version of a queuing system. When a map or a world you want to log into is at capacity limit, the game will ask you if you want to play on an overflow server - so you can actually play while you are in a queue," he said.
"Once space opens on your world, the game will ask you if you want to join your friends on your world. And you keep all the progress you made while you were playing on the overflow server."
Guild Wars 2 is currently in closed beta testing, and expected to launch this year.