After 30 days of your opponent not moving, their game will move into "waiting" and will no longer appear in the "active" list of your games. This is done so that your active list does not clog up with unfinished games.
If however you have not made a move in 30 days the game will still appear in the "active" list - acting as a reminder to make a move!
Currently nothing else happens to these games. On some sites the game will "default" and the last user to move will win the game (or be awarded some points). This does not happen on chrss, as it's a site for casual/friendly chess. Don't forget though you can always leave a comment to remind your opponent to move - they may simply have forgotten about the game!
updated: 2008-11-16 02:41:38
I suggest changing that to a lower number of days, maybe 14, or even 7. With regular people who take a break its not so much of a problem, but with the people who show up sign up for a game or two and then never return I find it annoying seeing them on my active game list for a month. Perhaps it could be set so that if there were less than four total moves in the game then it goes off the active game list in 7 days. thanks for chrss, its a great site.