One of the toughest things is learning the new technology. It's hard to pick up on all the new functionality available. I'm still floundering with MERGE in TSQL and I'm starting a major research project on spatial data, but I know there's other parts of 2005 that I haven't mastered and I'm implementing 2008. 2010.... blarf!
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning