I'd like to add a ring of mini M&Ms to the bottom half of a BC frosted cake. Think they will stay? Should I use sprinkles instead?

Also, the cake will be in the frig and then taken out to the party (outside) an hour before its eaten. Think taking it outside would pose a problem with their um, stickage (yes I just made up that word ?

That shouldn't be a problem. Here's a search of Google Images for M&M decorated cakes: http://www.google.com/images?hl=en&q=m%26m%20decorated%20cake&um=1&ie=UTF-8&source=og&sa=N&tab=wi&biw=1680&bih=933

I don't think the cake going outside will make them fall off if they are stuck in enough buttercream - though, depending on how hot it is where you are and what buttercream recipe you use, you may have a melting issue with your buttercream.

Also, I'm thinking the M&M's coloring may bleed onto your buttercream as they warm up due to condensation. It may be better to leave it at room temp before going outside to avoid condensation issues.

I used M&M's on a cake that I did a few months ago and they worked fine. I didn't put my fridge in the fridge though, so I didn't have to worry about the condensation. The only time that they started to fall was where I had added more icing to cover up a mistake. Here's a link to the pic of my cake if you'd like to see, they're the red and white "fans"

http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1684802