Defintely noticing the slowdown, but with the PC I'm using it's hard to tell if it's not just coming from my end; sometimes animated advertisements/banners/whatever can crash my browser, leading to the obvious conclusion that my computer is WAY past due being overhauled. Essentially, I'm not sure if the new look is just more demanding on my (very dated) computer's resources or there's other issues arising from it as well.
Fortunately, I have the parts together for the aforementioned overhaul together and ready to go; just waiting for my "expert" (read: a relative from out of town, though he is a certified expert) to get here in a few days, mostly because I don't screw up the (re)building of my PC. It'll be quite the upgrade, moving to a quad-core (from a single-core) and finally getting off of the memory-hogging Vista (didn't bother upgrading from that until I overhauled my entire system... which I'm getting around only now).
Tangential anecdote aside, there's definitely been a slowdown. Not quite crippling, but it's definitely notable. However, it'll be about a week before I can say if it is just on my (soon to be remedied) end or not.