I have them, both top and bottom. They're slightly heavier than the first wire I had a month ago. And YES, I can definitely feel them. I had no problems with my initial wires last month, but when they replaced them with slightly heavier ones last week, well... let's just say that I've had all kinds of discomfort and gum issues. My teeth and gums are super-duper sensitive now. Not really complaining, though, because I know they're doing their job.
You can also do a google search for "heat activated archwire" like I did, and I was able to find a lot of cool information.