Followed Andy Fore’s instructions on adding WP 2.9 to the whitelist.
The only problem I have so far discovered is Tag the Net doesn’t appear to work. The error:
Fatal error: Cannot redeclare class services_json in /home/path/wplog/wp-includes/class-json.php on line 115
Looks like WordPress distributed a new class-json.php. Back in Simple Tags 1.6.5, this specific error was supposedly fixed. My guess is something about WordPress 2.9 re-broke it.