In reply to needvert: I've been using the thermarest sleep system for a couple of years mainly for car camping with the kids. Although weight isn't an issue I use a luxury camp mat with fitted sheet, ventra down blanket and pillow.
In my opinion the system is much more comfortable than the traditional sleeping bag and the reason I bought it. As far as quality goes each item is of the highest quality as you would expect from thermarest so there don't appear to be any issues from being made in the far east which is where the majority of outdoor equipment is made.
We camp from early spring to late autumn mainly in the Lake District. During the colder months I just wear thermals and a hat. You wouldn't expect this system to keep you comfortable in temperatures it is not designed for. Where it really excels is in the warmer months where it is much easier to regulate temperature meaning you don't need two bags.
Also, I would have no hesitation converting this system to a light weight one for backpacking etc by losing the sheet and pillow and using a lighter mat which is another benefit of its versatility.
One thing I have noticed is this system doesn't appear to be popular here in the UK because most shops Don't seem to stock it though I don't know why.
I hope this helps.