Developer Rebellion has apologised for matchmaking problems suffered by players of the PC demo for Aliens vs. Predator:

Unprecedented demand for Aliens vs. Predator following the release of the cross-platform demo yesterday morning brought to light matchmaking issues on the PC platform resulting in players having to wait to join games, or even not find games at all. We're pleased to say later in the day the issue was corrected and a small patch to the PC executable next time you launch it from Steam will have you finding and playing games using Quick Match as it was intended.

While this issue did not affect the Xbox 360, we are, with SEGA's assistance investigating reports of a similar nature on the PlayStation 3 and working flat out on a solution. The full game features the ability to browse for and create games but for the purposes of simplicity the demo was limited to matchmaking, alongside the ability to set up groups with friends which mitigated yesterday's issues for many. We're really sorry that this issue tainted a day in which we saw many people get hands on with AvP for the first time and we're hugely gratified by the positive feedback to the game.