The threads on this shirt must have magic woven in because this shirt was so comfortable in both hot weather and cool weather (as a base layer). It feels weightless when you're wearing it, and in hot weather it keeps you much cooler than something like a cotton t-shirt. I wore on a trip that had both hot and cool weather, and it worked very well for those sorts of transitions. It's worth the price, because you just feel so darn comfortable in it.
Further evidence that Patagonia is more than just the 'it' brand of the moment among frat brothers. You might balk at spending this much on a shirt, but trust me, this thing is wroth it. The threads of this shirt must have magic woven in because this shirt makes you feel comfortable in hot and cold and everything in between. It's lightweight, so for hot whether it has a nice AC effect. I also use it as an base layer in fall and spring weather. It also has stood up to about a year and a half of frequent use and washing, and the material has definitely kept its color and has not shown any pilling.
I used this shirt most recently on my Honeymoon in the Mayan Riviera. after a long day in the sun i wasn't ready to head back to the hotel room, and wanted to stay in the sun. BOOM i popped this shirt on, and it was so light weight i didn't even feel like i was wearing a shirt. the pocket is convienent and i like the thumb loops. If you are looking for a good looking shirt to block the sun and keep you looking and feeling cool, this is the one. Buy it here, it is cheaper than the patagonia website, and you get points! JACKPOT!!!