In SQL 2005, tempdb management became a bigger issue.  Truthfully I did not do much to manage tempdb on my 2005 servers, placed it on a separate drive when I could and made sure it a couple of gigs of space and then ignored it.  However, I have noticed that in SQL 2008 temp db may need a little more careful watch.  On these beta servers, I have allocated twice the space for tempdb than I did in SQL 2005 and several times we have run out of space.  I suspect that some users may be trying out the new features of table variables a little more in-depth than our customers.   I have set up a trace on the tempdb so I can get a better idea of how it is being used and I will let you know what I find out.