Typically it has been all weekends in May and the first 2 in June. We were there June 9-13 and hit a SW Weekend in 2004.
My husband is a big SW fan and although we loved seeing the additional characters, we felt the event weekend was not that big of a deal. He wanted to buy the limited edition plush Jedi Mickey but we were told it was sold out the first weekend. (I don't know why they don't divide up the plush and other limited items and make them available each weekend, so that everyone attending has some chance to purchase them).
Most of the "stars" attending were lesser known/more obscure characters or people like conceptual artists etc. We expected it to be the big names but both years we've attended we were disappointed with the "stars" in attendance. (we went in 2000 and 2004)
On another note, to see the stars/get autographs, you have to get a fastpass and they limit it so fast passes are gone almost immediately. They usually have 2 stars per weekend.
