I am worried too. Since having my wii for about a week, the blue light came on last night at 2 in the morning and my roommate didnt know why so he put a pillow in front of it so it would stop glowing.
Mine is always on, but it does get a bit hot on the side, but I guess that's because I have it lying on its side! I used to have it standing but with my new TV stand it won't fit, so I have it on its side - if there was a major problem with this then I don't think you would be able to have it on its side (like they wouldn't have the rubber grips on the side so you don't lie it that way), so it should be okay.