[Joel]

The file formats between version 3 and version 5 are compatible, some things like tables and subgraphs, etc. will open in version 3 as simple groups, and the new bezier lines in OmniGraffle 5 will open in previous versions as the curvy line type.

If you upgrade your bundled version on your PowerBook now, you'll be able to use that license for OmniGraffle 5 on other machines, like a MacBook Pro.

Hope that helps,