[Lizard]

rllewis: Sorry I completely misunderstood. Yes, as a one-time thing you can have two databases open side-by-side. I just don't think it's a good long-term practice.

Export the database on one computer (give it a name other than OmniFocus.ofocus so you'll recognize it later) and transfer it to the other by some normal file-transfer means (USB thumb drive, network share, emailing yourself an attachment, etc.). Now double-click that exported file on the computer where you want to merge them, and it should open in its own window in OmniFocus. Then you can copy/paste or drag-n-drop from this file to your default database.