Despite being initially concerned about its very light weight and fabric, I'm sold on this piece. (The fabric type is such that I am careful not to take it off quickly or less-than-carefully.) I bought this as a base layer for winter, primarily for cycling use. I ride to work, so I'm guarded about bringing too much clothing, since the change in weather at the end of my work day means that I'll probably have to stow a piece in my bag. This shirt packs very small, provides several degrees of warmth, and is very flexible. If you're sensitive about having clothing right on your neck, though, you may want to find another shirt; I find myself tugging down the front of this shirt before I put more layers over it. Otherwise, great shirt.
I bought one last year and love it. The higher-than-ordinary-base-layer-shirts neck works great under a jersey for cool-weather road biking. I live in the mountains and long downhills can get chilly. I also wear it under fleece for staying warm in my poorly heated home. I think the sleeves could use another inch of length, though, but I do have rather long arms.