Wow, lots of great feedback here.
Timhhaan, Cyclezen - I'm doing these in my basement, where these days it's about 58 F. I actually have to keep an extra layer on until I'm warmed up, and that's when I turn on my big box fan. It probably would help to kick the fan up a notch when I get into the meat of a session.
Eric - good point about warming up for these beasts. I usually warm up 10-12 minutes before the first interval - enough to get a good sweat going. I'm sure it would be better to warm up longer.
At the end of a session I spin a couple minutes to get my wits back, then another 5 minutes or so to get my HR back down to mid/low zone 2.
Slim - I definitely don't want to burn out! I'm very gung-ho right now, but I want to make sure I can physically and mentally sustain what I'm doing.
I'll consider shifting some of my Mon-Fri work to SST. One of the (perhaps misguided) attractions of interval workouts was that I could fit them into a 45- or 50-minute window in the morning, before work. My impression of SST was that the sessions need to be quite a bit longer... maybe I'll need to get up a little earlier!
40x14 & Slim - point taken on rest & recovery. A few weeks ago I had a mechanical issue about 40 minutes into what was meant to be a long/hard Sunday ride, and wasn't able to put in the effort I was planning. The following Sunday I had what felt like the best ride ever. I thought I had a tail wind out - and back! So I've observed the benefits of rest; I'll try to anticipate taking a break every once in a while.
I'm also noticing that I need to sleep more than I did in the past... so I'm really gonna have to cut back my late-night bikeforums browsing...