Got my 18-55mm yesterday. Let's just say the 22mm spoiled me.
Low light focusing is extremely limited on the 18-55, where on the 22mm, it was hard to find something I couldn't focus on. AF seems kinda... uh, laggy? When you half press the shutter button, there's a slight hesitation that's not on the 22mm. AF speed after that seems similar, though. And yeah, it's definitely sharp enough for anything you'd ever shoot with the M, though the bokeh is a bit uneasy.
It's roughly 2.5x the length of the 22mm, so the camera's no longer pocketable with it on. Nice and smooth zoom ring, though, and extends pretty far, so it's nice that it was kept as compact as it is closed.
Like most kit zooms, it makes compromises, but considering there are only 3 lenses total for the system, it's definitely good enough for the price it's currently going for in the US (around $150 new). I'd say if you have the 22mm, go for the 18-55mm as well. If you have the 18-55mm, don't judge the camera until you try the 22mm, too.