I just got this today and hooked it up to my Dell 30" 3007WFP-HC monitor. When my MacBook Pro (2.4GHz 2GB RAM) is in better battery life mode it has a terribly flicker issue, but when in higher performance mode it works fine with a flicker maybe once every 30 minutes that I almost never notice. I figure the lower end graphics card accounts for the issue (it might not have the ability to drive at full resolution).
The adapter's USB port is hooked up to the one further away from the mini display port. I have only powered USB hubs plugged into the adapter.
So far I'm happy with this adapter and I do recommend it for MacBook Pro users.
I have an 30" Apple Cinema Display and this adapter works great for my Macbook Pro. It does provide a pass-through USB plug to activate the USB hub built into the ACD. Very happy to use my MBP at full resolution finally.