Though most of the other Google sites and applications work quite well w/ Opera, Google Wave is still not Opera-friendly...
Hope it is in the plans for 2010.
Links:
[1] http://linux.philosweb.com/drupal/category/it/browser
[2] http://linux.philosweb.com/drupal/category/it/google
[3] http://linux.philosweb.com/drupal/category/it/web