Never done it, since there are no mountains here - but I'd be willing to try it some time. Only concern is what effect such an enviroment would have on me because of my asthma. I don't have attacks, but being in cold weather tends to be hard on my lungs.
I dunno, what would some here say about that?
It's a lot of fun though, even if you can't get above treeline on your hike (below treeline on most mountains in summer is the same as it is at the base of the mountain, or not more than a couple degrees colder.). The biggest thing is just knowing your terrain and the dangers around. For example, Mt. Washington is one of the most breathtaking mountains around on a nice clear day when it's 60F in summer. The catch? If you see storm clouds coming, you'd better bolt for a hut or the base. Basically, above treeline on any given mountain is the most visually stunning by far, but also subject to the most extreme weather, and where rapid temperature changes can occur if something rolls in. Below treeline isn't any more dangerous than hiking through a normal forest (generally). So, if you're more susceptible to bad weather, you just need to be alert and know when to wait for another day. That's honestly the hardest part...knowing when to pack it in, and try again some other time, especially when you're "so close" to getting to where you wanted to reach.