I've just had a look at the flag module rules integration. While developing it, I found a bunch of bugs in rules I've sorted out now - so make sure to install the latest beta5 when you try it.
Flag module is great, it doesn't allow "just" AJAX flag links, but also flag links with confirm forms containing custom messages - this is great to build an easy way to manually trigger rules for nodes, comments or users. Clearly this is the successor of the "old" drupal 5 cclinks module which shipped with workflow-ng, with which I tried to solve the same problem. The scheduling features of cclinks has rules built in anyway :)