Probably second only to navigating to a specific forum. Probably even first for most of us. Adding clicks to access the most used features is just inefficient design. I can resolve the added clicks to get to specific forums by subscribing to them (at least on my laptop). But there's nothing I can do to avoid two clicks every time there is a response to my post . . . which, of course, may not be a response because it could be a new post in a forum I've subscribed to solely for the purpose of being able to get to it in a single click - or, heaven forbid, a new post by a person I've subscribed to.
Most of the rest of My Stuff is used occasionally (at most, I'd guess, once every few visits - as opposed to My Posts, which I use several times each visit if I'm actively posting). Why not give My Posts the upper right link? It can still double as the sign-in link, since when you aren't signed in you don't have posts. Move My Stuff either to a link within Navigate - after all, it's just one more thing I need to navigate to occasionally - or to the upper left box where all the rest of stuff related to me lives.
Where to find things - I'll get used to. I've been using computers since the 70s, and have moved from DOS to Windows, from Clevenet to the wide open internet, and through multiple iterations of word processing/spreadsheet/graphic/etc. software. But what my experience tells me is that while I'm pretty tolerant of subjective change, I'm pretty grumpy when the change objectively creates more work for me even after I've retrained my brain as to the new paths. (Both the vast quantities of white space (added scrolling) and added clicks make this objectively a less efficient site.)