Well pretty good, at least.
Received it this morning at 9:20 from Amazon. Installed it immediately with some hitches, but now all is fine.
Let me start by saying I purchased a full version of Ultimate, 2 full versions of Home Premium and 1 Upgrade version of Ultimate. The full versions installed without any notable incidents. The Upgrade version was a bit fussy. Not only do you need to have XP installed on the machine you are upgrading but you must also start the installation from inside Windows XP. There you are given the choice of upgrading of doing a clean installation.
A small hitch with my ATI Radeon X1600 video card in one of my systems was quickly fixed by downloading and installing the latest (01/28/07) driver from AMD/ATI site.
Now, all systems are go. It's only day one, so there still may be small problems popping up as I go, but I don't really foresee any since I ran both betas, both RC's and the RTM on all my systems over the last year or so.
So far, so good.