Great book, I bought it recently and have just finished reading it. I'm a big fan of the Hijax approach, especially if you read my comments on the 'Twitter' post back over in the General Forum.
With regards to using GET or POST, I think it's 50/50 and depends on the situation at hand. For something as simple/standard as a ratings system I don't think there would be any issue using GET to submit the values. As mentioned before, POST is more favourable when submitting large amounts of data and/or you need to 'hide' the data inside the request instead of them being sent attached openly to the query string.
Jeremy Keith is a big standardista so he will always take the route he deems right, but I don't think there is anything 'semantic' so to speak about your situation and whether using GET or POST really makes a difference, although JK might argue otherwise?
If you're happy with using GET then stick with it. I personally don't see any advantages to using POST here.
- Mike