I'm not sure the dates for Star Wars Weekends have been released for 2011 yet. In 2010 they were from May 21st thru June 13th - ie. every Friday, Saturday and Sunday through those dates. It'll probably be similar though as previous years always have been.
The other parks aren't usually impacted by the event but Studios is obviously a lot busier. If you're just at the park doing your thing in general then it's not going to be to bad (I was there one time but I'm not into SW that much so didn't check out that much, just the parade iirc) but if you want to do anything that involves the specific Star Wars events expect it to be a bit crazy. Fairly sure I heard of people camping outside the park this year, sometimes as early as the night before/wee hours and lines for photo's, etc will be long and you would likely need to plan your day carefully to make the most of it.
