I have done the "jacket and bivy sack" thing many many times. Usually to get some shuteye after coming off an alpine climb, or to grab a few zz's right before starting one.
These "mountaineers" systems are generally not suitable for a long night's rest, because the whole concept is based on the mountaineer's mentality of a "bivy" camp, which is not a long sleep.
One memorable moment: Alan Dixon and I climbed (oh wait, I mean attempted) the Middle Teton, we opted to ditch overnight gear. We both had GoLite Coal jackets and bivy sacks. I used an Ortovox "Bivvy-Poncho" and Alan used an ID Endurance, I think. We started at Billy's Giant Hamburgers (calorie loading), sorted our gear on the lawn outside the Jackson Hole Visitors Center, then hit the trailhead around 11pm, after a long day of travel.
So, being able to hike for a few hours and then sleep on the trail for a few hours was a nice option, because the alternative was to sleep in town in a motel, which as you know are not very appealing because of the warm bedding, access to hot tubs, and fresh pastries in the mornings.
Anyway, the temp was around 33F and needless to say, our nap systems were dialed in so perfectly that the cold woke us up exactly at the right time so we could continue hiking and reach the base of the climb at dawn.
Yep, the bivy-jacket thing is the way to go sometimes.
I've climbed Gannett Peak (WY) and Mt. Olympus (WA) in this style as well - using a jacket and bivy combo. The approach is around 18 miles, then a climb, then the hike out. On both climbs, I started at around 9 pm, hit the base of the climbs at dawn, climbed and descended by noon, napped in the "warm" (relatively) hours on the way out, and finished back at the car around midnight.
It's actually a really fun way to climb a remote peak, or just visit a remote lake or place even, without having to plan a weeks vacation around the event.