The 6.5 Groupwise client is great - apparently it's had the bulk of the work and improvements on this version. It's a lot more outlook-like in many ways, and certainly much tidier and more modern looking.

GW7 is yet more polished, but I haven't spent any significant amount of time using it yet. There's proper, native PDA syncing support and these days the Blackberry server-side stuff supports GW6.5+ too. I don't think the typical email user who was used to Outlook/Exchange would find much to complain about these days.