Couple of days now and I have to say, this mouse is absolutely fantastic. Every time I grab it and use it, it just feels so comfortable and smooth... probably the most comfortable mouse I have had since the MX518.
So far I haven't found a great use for all the buttons, but as I get back into AutoCAD, Fusion and Visio... I'm sure I will find uses for all of them with some custom profiles.
So far I only have 2 profiles, desktop and game. Desktop has the top side, and bottom side buttons doing the same thing. Browser forward and browser backward.... just doesn't seem worth it having those doing anything else on a desktop.
That said, unlike some reviews I have seen, I haven't found the cluster of four buttons to be awkward or difficult to navigate at all. It's actually VERY clear which button you're about to press. The only daft thing about it is the modifier button below it. Now this button is great for a low DPI (e.g. sniper) button, but as a modifier it seems a bit silly, as when you're pressing it, the only buttons you can comfortably reach are LMB, RMB, and MMB... at a stretch you can reach the DPI and profile buttons, but its a bit awkward. I'm sure there are some MMORPG games where this would make sense, but to me it just makes sense as a button rather than a modifier. This is all choice though, it's configurable, so no points dropped.
I might experiment on the desktop with some windows desktop features (Task View, switch desktop up/down) and see how it works.
So far its a 4/5 for me, and only loses a point for the software being a bit poo and crashing during initial config and upload.