My friend's gets pretty hot, and I remember a Dell we used to have got so hot I could have probably cooked on it, but I never noticed any real issues. Keep it away from flammable materials I guess.
What are you doing when its getting that hot? and where is it sitting? on carpet/tiles/wood?
I've found that mine is warm-ish to the touch when my macbook is just surfing net and doing idle-ish things like that. However, when charging the battery (and obviosuly drawing more current) it does get noticeably warmer, and then when doing intense things like folding@home units, encoding or gaming it does get hot but that is expected it is drawing alot more heat. Just imagine having a 85w light bulb in a small enclosure...
The heat won't be a problem, but if it does concern you, just sit it upright on the floor as long as you give the cable enough length it shouldn't fall over... unless you have something like shag carpet which you shouldn't be leaving the AC adaptor on in the first place!