There are 4 major celebrations that you will expect to have lots and lots of people:
1. Makha Puja day
-the date for Makha Puja is not fixed. It follows the Thai calendar
2. Anniversary of the passing away of Luangta's mother- 31 May
3. Luangta's Birthday- 12 August
4. Kathina (normally end of Oct or first/second week of Nov). For year 2008, it will be on 18 October 08.
Therefore, if you are there, do expect there will be a bit of problems with the sleeping arrangements. You may want to consider booking a hotel/inn in advance- because accomodations may be fully booked since many many people come to participate in Kathina. For instance, a friend of mine had booked 6 buses from Bangkok to Udon Thani- they arrive on Saturday morning and go back on Sunday afternoon. And many others are doing that.
Normally, others will be sleeping at the halls. Female quarters will be expected to be full because places are very limited.
Still, kathina is a very auspicious time- to perform offering and dedicate merits, especially for your parents, a sick family member, etc.