Yeah and using R, S, & A have been cutting it for a long time but now im doing a lot of work where i have to switch very very often, to the point where I'd want a Modifer key like I do for the Pen tool.
Thank god for that tho, I couldn't stand having to go from A all the way the P every few seconds, A to R is hard enough right now and they are close to each other...
My solution for now has been to map the Roll tool to X, which is significantly closer, and i never really used Mark Clip anyway, I prefer Shift-A for things like that...