Simsi - 6:46 pm on Jul 1, 2011 (gmt 0)
Considering how good Google seems to have become at LSI recently I can't see it would be too tricky for them to remove the noise from the bounce rate signal.
The argument that says a user may find what they want in a "quick hit" sounds reasonable enough but the user's behaviour prior and subsequent to that specific visit will probably tell Google a lot more. The arguments about sending wrong traffic to the wrong pages etc... similarly.
Personally I think bounce rate might well be a good strong signal but not necessarily at "site" level, more at page level and factoring in Google's analysis of (grouped, not singular) user behaviour around the time of the search.