I wear fox pro D30 pads on every ride. They don't give me any discomfort so it would be foolish not to. On a really warm day they can get a little hot but I'd rather that than destroy my knee.
I'm using TLD speed pads, they're pretty much knee warmers with a thin pad. At the moment while it's cold I wear them all the time but usually I put them in my bag until I finish my commute to the trails.
Alpine Paragons here and I wear them for all trail rides during the entire time. They're pretty light weight and don't bother me too much. They are however starting to get a bit loose since they're a couple of years old. Gonna give them a wash to see if it helps, otherwise I'll replace them soon. On XC fitness oriented rides on my hardtail I don't wear knee pads.
Kind of depends on the ride I'm doing. If it's for mile munching and spinning my legs without putting any serious downs in I'll go without. But if I'm having a bit of a gravity orientated day, kneepads all the way.
Pads and a helmet are the only protection I really wear. Only injury I've had (so far) is a broken wrist, don't think any protection would have saved me there.
Have some pretty heavy duty trail pads that I wear almost all the time. I take them off and put them on my bars if I’m going to be climbing for more than 20 minutes straight on an enduro style ride. I have been saved numerous times by my pads and my knees are quite scarred up from my riding before getting pads.