I stayed in the Gritti about 3 years ago on a *wood reward. I was a little disappointed -- perhaps because my expectations were so high. They gave us a fairly crummy room. It was nicely decorated, but small, and faced a wall a few feet from our window. We firmly asked if they had anything else, and they claimed not to. We were even willing to move the next day, but no luck.
I also did not think the public areas are particularly impressive. On the plus side, the staff were friendly and the location for sightseeing fantastic. If I were going in the summer, however, I might prefer (location wise) one of the *wood properties in Venice that had resort facilities.
In short, my opinion is that Gritti's reputation and history may be better than its reality. We'll probably try someplace else next time we go to Venice, especially if it is cheaper or fewer ff points. I've heard the other properties are BETTER than their reputations!