Jason,
I just picked up a pair of the REI One Pant as a Christmas Present.
(They are marked down from $185 to $129).
Here are my thoughts - I stay pretty warm in the winter, and sometimes struggle between what to wear as a pant. I have my 8-year cordura hiking pants that are great in spring and fall. For winter hiking and XC-skiing, I usually wear a pair of TNF insulated tights and then sometimes a windpant over them. However, I have been looking for something different though. I'd like something that offers a looser fit, but is still pretty stretchy.
I don't like fleece pants for hiking skiing or climbing (as Mike mentioned) the snow does not brush off well. I perspire quite a bit inside normal nylon windpants when over my tights or fleece pants. I don't think my goretex pants breath well enough, even when unzipped to want to wear all day.
I started looking at these and thought they would be great as an all conditions pant for winter. I can still easily throw a goretex or wind pant over them on the windier summits, they have zip close pockets to put a couple of minor items into and at camp at night I can pull a pair of primaloft pants over them for full insulation (OK, if I ever get AROUND to buying the Primaloft pants). I probably would not wear them in the summer.
As a jacket, I don't think I would get near the range of use that I would from the pant. I wear a midweight smooth-finish stretch fleece that allows snow to brush off completely and air to circulate freely and since my upper body puts out quite a lot of heat (I am a big guy), I am afraid the one jacket just will not be breathable enough.
If anybodyt has some better ideas, please toss them out, as I think the $129 is quite a lot, but then again, if they last me 10 years, that's only $13/year