The slow booting was about having to select the correct boot disk; the problems with slowness seem to be related with the Airport drivers (or Flash or w/e) which will most likely be solved soon with new updates from Apple; same for flickering in some iMacs. Tons of people having no problems at all. Also, mass manufacturing always brings along some problems. Just buy it if that was your plan; in case it doesn't work as it's supposed to you can simply switch or return it.
The nice thing about Win7 is that it isn't awful. I'm running it on a ThinkPad that came with Vista and I would never (EVER) switch back to Vista. That being said, there is nothing in 7 that makes me want to upgrade my XP gaming rig to 7.
My day-to-day machines are a 15" MBP running Snow Leopard and I just bought a 24" iMac refurb... neither running Windows.