I've spent hours trying to figure out how to assign Mouse 4 or Mouse 5 to shift, option, control, and so forth, with no success. I'm almost positive it is a Mountain Lion (or Lion) issue as my previous Kensington trackball wasn't able to do this either. Figures back in Mac OS 7-9 all of this was working on Kensington mice. Right now I'm speaking from a Razer Deathadder Black 3500, which does have functional Synapse 2.0 on my Macbook Pro Retina 15". The best unusable solution I've tried is creating macros in Synapse which say use shift key down, delay X seconds, then shift key up. However it's very impractical and causes what I guess is ghosting, if I'm playing a game like WoW my character will start spinning out of control. This also happens if I use the simpler keystroke assignment to Shift (which doesn't work anyway) Not just whining about games though, I'd like Option to be one of the buttons for various keystroke combinations in Final Cut Pro as well as option+click can hide an app. In finder the latter DOES work if I bind a button to option click, but nothing else does, in order words in text edit what happens is a crosshair cursor appears holding down this option mouse button (working) but typing doesn't result in ƒå∂ßƒ, etc. Search results showed multiple people with this problem, some blaming Razer/Synapse, or WoW, but honestly I think it's because people just buy Razer stuff and play WoW as opposed to testing any other brands/apps on ML. I've tried KeyRemap4Macbook & attempted coding xml, USB Overdrive 3.02 (same results as Synapse), various Synapse settings, and pre-synapse Razer driver settings, so far nothing. If USB Overdrive had more functionality like programming mouse5down to shiftdown and mouse5up to shiftup maybe it would work? Any help would be much appreciated. Thanks!