[jdh]

Actually, it's more a question of whether you share the same iTunes Store account. As with media content, you can have up to five computers authorized for the same iTunes Store account, and ergo can have up to five computers authorized for the same App Store items.

If you're syncing to different libraries, then simply find the OmniFocus.ipa file (should be in your "Music/iTunes/Mobile Applications" folder) and copy that to the second computer and import it into the iTunes library on the second computer in the same way that you would for an audio track (ie, File, Add to Library or just drag it onto the iTunes window). Once in your second iTunes library, it will sync to your second iPhone in the same way that any application purchased on that computer would.

In fact, you could also just attempt to re-purchase the app on the second computer. As long as you're using the same iTunes Store account, you'll be notified that you've already purchased the item and can download it again for free to that computer (this is different from media content, which would need to be re-purchased).