OK, so I've made 2 cakes with perishable fillings and had to store them in the refrigerator overnight for early morning deliveries. I was sad to find that the next morning when I take the cake out, it sweats!! 
It looks all slimy and gross and I was so not happy when I delivered it! Thankfully the customer either was nice and didn't say anything, or they weren't phased by it.
If I'm finishing a cake the day before it's due and there is a perishabe filling, how do I avoid this disaster again??? Does the condensation go away after a few hours? Is it ok to leave a cake with a perishable filling like mousse out for hours so the sweat goes away? 
I'm sure this is an age old question, but something I haven't encountered yet, I usually ice a cake the day it's due.
was it covered in fondant? If so that is totally normal, just stick it in front of a fan, DON'T touch it, and let it dry. If it is BC sweating...well I'd think a fan would do the trick for that as well. As far as leaving the cake out, it would depend on how long it was in the fridge. In the case you mentioned overnight, you should be ok to leave it out for a bit to get the sweat to dry, however you do not need to leave it out for a few hours if you put a fan on it. I wouldn't recommend leaving it out for that long.
HTH 
hmm, was it covered in fondant? I've had fondant sweat before and yeah it goes away after a while. I just don't try to remove any moisture 'cause the one time I did, it kinda started to smear. Maybe check the temp on your fridge and make sure it's not super cold in there. I have a seperate fridge I use for cakes and I adjust the temp to factory setting, so it's not too cold.
Are you covering in fondant or buttercream? I find that my fondant usually sweats and to be honest I try to avoid putting it in the fridge.. I just tell my customers that fondant shouldnt be refridgerated and that the fillings that should be refriderated shouldnt be used with those cakes. If there is an easier way I would love to hear it because I just had to persuade a bride that wanted mouse filling for her fondant wedding cake for that very same reason..Didnt want her cake to sweat and get all mushy. So I talked her into strawberry filling instead. So I dont have to refridgerate.n I cant wait to read the resposes you get for this one.
Yes, when it's hot out and you take the cake out of the fridge your cake is going to sweat...it does look kinda gross but, like the others have said if you put a fan on it it will be fine.
I have done this once with fondant and it took a couple hours to get the sweat to go away. And yes, you should make sure you are doing non-perishable filllings when using fondant. I also have my bc sweat when it's too hot. I just put it back in the fridge! But, I am sure the same with fondant you could put it under a fan.
Anytime you take something cold out of the fridge into the heat it is going to sweat.
I used buttercream. Also, I have to say that I think it's happening more since the whole "crisco" fiasco! I changed my buttercream first to the zero transfat, then hated that and then went to store brand shortening and my icing was back to normal, but now it's sweating..... 
Maybe it's the change in temperature too because it seems as if my buttercream is a little more greasy as well.....
OK THAT'S IT, I HATE MY BUTTERCREAM!!!
I'll have to experiment with the fan and new icing recipes...I'm in New York and humidity is awful and can be horrible for cakes! Plus I'm still learning, so it's hard.
Thanks for all the help.
I just had this same exact problem!
What I learned is that if I take a cake from the fridge (bc or fondant) and it's warm in the room, it's GOING TO SWEAT.
What worked for me is to turn on the air conditioning and cool the room before hand and then take the cake out. When I did it like that, it was fine.
The buttercream did eventually dry out, but it took a while.
If you don't have AC, I would try the fan. Should work.
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