That depends on how often you're changing files on your system. Time Machine backs up until the Time Capsule is full, then will start deleting older backups to make room for new backups.
One problem I've come across is virtual machines that write to a large image file rather than using a partition for the OS. If you're using a virtual machine (ie, Parallels Desktop with Windows), you'll want to make sure that the folder to which your virtual machine saves its image file is excluded from the backups.