To throw my hat into the ring, I too, suffered from problems with my Drobo Pro (8.5TB of data) as soon as I upgraded to Lion. Drobo told me to use disk utility, disk warrior and then asked me for a bunch of information. I didn't bother responding because I just felt I was getting the stock "customer support" boilerplate and just didn't have time to address it all.
THE PROBLEM: upon upgrading to Lion (and encouraged by the Drobo website affirming Lion compatibility), the drobo pro connected via iSCSI would hang the entire finder. The only solution was rebooting upon which the system would hang shortly thereafter. Time Machine would also hang and generally, this was not working. So I disconnected the Drobo Pro and effectively stopped time machine backups for almost a month.
Browing the drive was impossible.
Time Machine was non functional.
SOLUTION ATTEMPTS:
Disk Utility in Lion would hang and never complete.
Disk Warrior in Lion wouldn't find the drive
All firmware and dashboards were upgraded accordingly
I tried connecting to Firewire 800 vs. SCSI and that did not work.
FINDINGS:
I plugged the Drobo into a Snow Leopard MacBook Pro I have lying around and voila, everything worked perfectly fine.
Ran disk utility: reported no problems.
Ran it again, just in case: no problems.
In SL: Streamed HD video files from the Drobo: no problem
In SL: could browse the Time Machine backups: no problem
THEREFORE: the problem is a conflict with Lion and the Drobo iSCSI and FIREWIRE 800 interface. I haven't tried USB on the Lion MacPro, but frankly, even if it does work, it will not be a good solution for my workflow due to its excruciatingly slow pace. I bought the Drobo Pro for iSCSI interface not the pokey USB.
That's about it. Let's hope they get this thing fixed ASAP. So far, the only Lion-related problem I've had.
-JP