Well, I think the tagging plugin should be revised. Two of the problems I see on the surface are that it doesn't escape apostrophes and that if someone changes their name after you tag them it will stop the page from loading.
Code:
@"Hel'lo"
1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'lo'' at line 1