I pulled some data today on tablet PCs from Amazon that I used to create the above graph, which shows the number of ratings and average rating across all reviewed tablet PCs by manufacturer. I filtered for tablets priced between $75 and $1000 and removed duplicate information across variations of models (e.g. same reviews/ratings across different versions of the iPad 2).
It’s very rough, but I still thought it would be fun to share. I wouldn’t feel comfortable making any conclusions from it outside of the fact that Amazonians that review their tablets seem pretty happy overall with them (~75% of the ratings are above 4 out 5).