For those of you who purchased OmniGraffle 4 or OmniGraffle Professional 4 from our online store on or after October 31, 2007; you should have received by now an email from us containing your new license key for OmniGraffle 5. If you haven't received it yet, please let us know.
For those of you who purchased OmniGraffle 4 or OmniGraffle Professional 4 from a retail outlet or online store that's not us, if you contact our sales team at sales@omnigroup.com and provide some form of proof-of-purchase, they can help you out with getting a free upgrade to OmniGraffle 5.