akon is right. If you treat your machine nicely and don't do hard shutdowns (holding the power button until the machine forces off) and force quits then you should not need to ever repair permissions. However it always does not work that way.
As for weekly and monthly maintenance,
OSX by default runs daily, weekly, and monthly maintenance processes. Just keep up-to-date with all updates, avoid suspicious downloads, and treat your machine kindly.
Also consider the free utility,
Onyx as the panacea for all your maintenance concerns.