Ummm...so the newest version of Outlook (2007) isn't quite ready for the 2+GB ost size? I've got clients and users that are routinely over 5GB and some to 20GB....and there's no telling them they can't have that much email when they just footed the $50K-$150K to upgrade their mail system to the latest and greatest. Integrate the UM aspect of E2K7 and watch the MB sizes grow.
I've got a similar scenario to Matt's post whereby the laptop ost load is slow....and I've got a 7200rpm drive. The OST is 2.5GB. There should be a method where the OST only loads the inbox and (maybe) the last 5 folders used....that way it blasts open....then in the background, it can more slowly load the remaining folders/items unbeknownst to the user. This might be the interim workaround instead of waiting to load a whole OST.