My "to date" combined mileage for the Si is about 27MPG.
That said, in the last few months I have been using my Scangauge to 'hypermile' (not really, but close) the Si, easily getting into the mid to high 30s on several tanks (average 36.5 MPG over last 7 fills). It would be higher if I didn't ruin it with spirited driving here and there (but that's the whole point, right?)

/Dances a jig for this thread (happy gas thread nazi shuffle)