During import it's possible to get the gravatar check done, however, with massive big forums, it's a drag to do. So we opt out. however, when later the import tests are done and the site runs and ppl have chosen their avatars etc, there are enough ppl left who might have gravatar, but haven't picked an avatar "yet". A "sync gravatar" option that does per 250 a batch and lets you quit the process, but resume at a later stage (remembers) would be really awesome. Then a monthly "lets run through a bunch" would become possible and making this a more managable task.