This happens to mine too! The genius bar guy acted as if i were crazy when I said 100c - he's like "you do know that is hot enough to boil water, right?" (yes lol, i'm familiar with water's boiling temp...) I also use Temp Gauge (from the ap store) to watch temps. I've had my mac no more than 2 months, and noticed right away it got super hot when doing almost anything with it. Even youtube or hulu raise to 100c within seconds. I'm scared to play any games on it at all, which is a total bummer as I went with the stronger hardware so I could do some light gaming...
I took it to Apple and they checked it out and say they "could not replicate the issue" which is odd, as almost anything I do gets it over 90-100c. They did a factory reset and told me it might be because I transferred a bunch of music files from my other pro. Really? Are they really that fragile that music files corrupt the entire machine so it overheats? This was not a problem before... I have not put any files back onto this machine but it still runs super hot.
The fact that multiple peeps at Apple have reported no familiarity with the fact that these run hot (even though it's all over these and other forums) and were not able to see what I was talking about when I brought it in worries me. I bought this as I needed something more than my Air for school work, and am worried it won't last long if it runs so hot all the time. Of course this is the one time I didn't get Applecare as I've never needed it on my several other macs... fml lol.
Hopefully they run a patch for the OS or something that fixes this? Fingers crossed... : /