Mix07

Go to MIX07 April 30 to May 2 in Las Vegas and get a copy of Vista Ultimate for free

I went to Mix06 (before I was working at Microsoft - well, I actually worked for a vendor, but also got to see quite a bit of the conference).  MIX is fun, filled with interesting people and you'll pick up some useful info about producing innovative content for the web as well.  Here's a tip, if you want to "balance" your time between attending the conference and enjoying Las Vegas, you'll want to make sure at least to go to the keynote by Scott Guthrie - the guy is just a 'brainiac'. 

Note that Mix07 has content for both web developers and web designers - a session list is available already.