I'm a recent convert to OS X and work in a company that, until very recently, had a very MS Windows oriented IT department. I found Groupcal when I was scouting around for ways to avoid having to install more MS software on my shiny new MBP. Conceptually, it sounded perfect.

Functionally, Groupcal does pretty much everything I need. It reliably synchronises my Exchange calendar and iCal so I don't need Entourage :-)

My main gripe is not really a problem of Snerdware's making. SyncServices in OS X are horribly flaky and susceptible to multiple apps trying to sync at the same time. This has meant that I've had to call on the services of their support department a few times in the 6 months or so I've been using Groupcal. On the positive side, support is always very responsive and I have been given patched versions of Groupcal on a couple of occasions to fix my specific issues within a day or so of raising the issue.

Overall, I think that groupcal deserves a solid 4.5/5 losing the 0.5 for some of the challenges that are introduced by SyncServices when upgrading between versions of Groupcal.

My recommendation is to buy this product if you're working in an Exchange environment but don't want to be forced to buy Entourage $$$. Be prepared to assist the support guys in troubleshooting and you'll get fantastic response. It's well worth it.