Well, for most guests you'll have a few daily shots at getting autographs, but be prepared to check in often at the "Walk of Fame" area and find out the signing times for your favorite guests, and then plan to get into line 15-30 minutes (or longer) for really popular guests, or not too long for the not-so-popular guests. Sometimes you just get lucky being at the Walk of Fame and the guest shows up and not too many people are there at that time (due other in-demand panels syphoning away fans from the Walk of Fame).
For this year, the big guns were Patrick Stewart, William Shatner and Leonard Nimoy. Those lines were pretty long (with Patrick Stewart signing in another room all-together away from the Walk of Fame just to keep the line congestion to a minimum. That also did the same with Shatner and Nimoy during the few hours both gentlemen did their signings on a couple of the days. So, that freed up line-space for the other guests, and most lines were going well, though the lines for the Battlestar Galactica guest tended to clog up the area during their signing times. John Schneider was ridiculously busy, but he knew how to work the crowd, and the ladies loved him for it.
But that being said, the best day to get autographs is probably Friday as long as they show up somewhat early in the day (after lunch at the latest). Plus, once you get your signing business done on Friday, that frees up your schedule and convention itenerary for a more relaxing experience.
Now, the prices for the autographs can get crazy, so be prepared for sticker shock for some of the celebs. Shatner and Nimoy commanded $75/signature with no personalizations. Patrick Stewart was near that level as well. But most range from $25-40, but the contingent that is represented by Julie Caitlin Brown charge extra for the glossies (like $10-$20 per glossy photo), while most other celebs don't charge extra for the glossie, just for their autographs.
Some guests are really nice about taking photos with them at their tables (like Doug Jones John Billingsley, Anthony Montgomery, Eric Roberts, and others will allow for a quick photo if you buy something they are selling at their table), but if they are signed up with a professional Photo-op deal, like with Froggy's, then they don't do photo-ops at their table and you have to buy a photo-op with Froggy to snap your visage standing with your favorite celeb. I think they give you a printout of the photo, and the photo file as well for the service. Here was this year's menu of photo-op pricing:
http://www.flickr.com/photos/patcave/3907643896/
