So… according to Matt’s post, WP 2.9 should be released very shortly. I’m releasing Version Checker 2.0.2 as a result.
The latter disables core upgrade nags for non-bug fix WP releases. Experience has shown, in past years, that major WP releases need about an extra month of testing in the wild to be really stable. You can still upgrade, when WP 2.9 gets released, under Tools / Upgrade. But WP won’t nag you into doing so.