I'm really getting to love GMail, and it's interesting to see the targeted advertising (which is pretty subtle) appearing. However, I'm completely taken by PGtGM – and I just hope that Google doesn't close the web-service side of things (that this uses).
From Google's point of view, it's hard to see why they wouldn't shut this down – I mean, unless they start inserting advertising-links directly into emails, they're not going to get many click-throughs are they!