I've used this base layer in a range of different temperatures (not just on hot days, as the description implies) and found it to always be comfortable. I usually use this anytime it's over about 50 degrees F (below that I'll use something more substantial), and have used it on 90-95 degree days as well. The description on the CC site really says it all - great wicking, great fit and no extra bulk. I have about 4 or 5 of these that get rotated through the laundry, and they've been good for about 2 years so far - with no signs of significant wear.
I wear a Large - am 6'4", about 170 lbs. The length of the base layer works well (it's not too short), and it's a nice fit without being suffocating.