Sleeping shirt?

It depends for me. On shorter (weekend trips) I'll usually just sleep in my hiking shirt. If its warm enough and there aren't many bugs I take it off and let it dry and bit while I'm in camp. On the one longer trip I've done I brought an extra shirt that I rotated wearing to bed and hiking. That seemed to work pretty well for me.

Adam

i bring along a very lightweight silk shortsleeve or longsleeve shirt for sleeping

Since I wear a loose shirt, it dries and I put on over it my insulation layer and my windshirt for sleeping.

I like to sleep in a long sleeved lightweight shirt like a Patagonia one for two reasons; to keep the bag clean and I do not like the feel of nylon against my skin. Also because of this I like to sleep in silkweight longjohns. It is also easier to get up in the middle of the night to heed the call of nature. On with the shoes and maybe a jacket and off to the woods I go. Both of these items are for around camp wear, but not for hiking.

Randy

In warm weather, I simply sleep in my hiking shirt (an Airius T-shirt.) While it's sometimes damp when I get to camp, it's always dry by the time I've cooked supper, set up my tent, and sat around chatting or contemplating my navel for a while. In cooler weather I'll sometimes add a pair of light or midweight longjohns (top and bottom) – and this may be the same pair I've worn all day, depending of how cool it was. Again, they've always dried by the time I'm ready for bed.

I have the same "standard" gear, occasionally minus the vest if it's warm enough, and always sleep in it all–mostly a convenience/efficiency thing. I like to just get up and be able to get moving in the morning. I don't think I ever stink too much (thanks to the wool) and I prefer the wool on my skin over nylon.

I sometimes have only one shirt. Typically on trips where the weather is expected to be very moderate (35-55F) or when I am trying to go SUL.

I have never had a problem with it being too sweaty before going to bed because it dries very quickly (powerdry or coolmax featherweight). I have gotten under the covers when the shirt was soaks by rain, but found that it dried pretty quickly once I was out of the rain and my body could heat it up.

Most of the time though, I bring a second shirt. There are two reasons. In warmer weather it's because my daytime shirt (supplex) starts to stink and isn't the most comfortable thing to sleep in. So I want something less smelly and softer. In colder weather I was more insulation fo my arms than my daytime shirt provides. I have been known to use my "sleeping shirt" during a hike when the weather turned out to be surprisingly cold… so I really treat it more like a light insulation layer than a sleeping shirt.

–mark

Ditto those folks above with a sleeping top plus a bottom. With my last six trips I have brought along on all a Smartwool top and bottom; short-sleeve or long- and brief or full leg. With weight grade of the top and bottom based on night temps.
As mentioned benefits by other posters: 1) the comfort of "fresh clothing"; 2) the lack of stickiness inside the bag and 3) with a down bag, no added abuse to the down.
I discovered these benefits after bringing along a lightweight top and bottom during a 2005 trip to make up the warmth of only having a 32 degree rate sleeping bag with temps in the low 20's. I slept wonderfully not including the warmth factor.
Now I look at the extra clothing like a second pair of socks which I always carry. It's good to have a back up in case an article of clothing gets too wet, or even damp, to dry out.
But like Adam mentioned with weekend trips, it may not be worth it or if the weather is moderately warm that your top and bottom dries out in time for bed. Though I still like the "freshness" going to bed in clean clothing.
In short, just factor an extra top and bottom based on the sleeping bag/quilt and pad you'll bring and the nighttime temps. I bet you'll like the benefits vs the weight added.
Aside: Early this year I emailed Smartwool whether they had any data on degrees of warm added to a sleeping bag with their tops and bottoms. And though they responded quickly, they had never did any study on such a factor. But still I would rather add warmth through extra clothing than a sleeping liner or top bag.

For warm weather I bought a cheap silk top and bottom. They are paper thin, probably weigh 150 grams total (shamefully, I have not weighed them..), and pack to the size of a cliff bar.
In cold weather my wool 1 top and bottom dry out by the time I finish rehydrating dinner; and merino does not stink too bad..

> For warm weather I bought a cheap silk top and bottom.

I couldn't find any, so I bought a few metres of 8 momme silk from ThaiSilks and made my own. Roughly like pyjamas or track suit, with hood to protect the sleeping bag too.
Works great with a quilt!

I've switched to a very lightweight WinterSilks silk top and bottom set for sleeping. Very comfortable and keeps the bag clean too. Just had to have the camo (the photo is from the online catalog).

My full three season clothing set includes a silkweight polyethylene long johns and long sleeve top (Patagonia or GoLite). I perspire heavily and an extra shirt makes life more comfortable. If I'm looking to hiking a long day in cold rain, wearing rain pants with long johns under makes a great combo. And it leaves the shirt and long johns as a sleeping option.

Another part of my clothing set is a Mountain Hardwear Powerstretch top, which also makes a great sleep shirt.