I agree with Jeff - I user a stir plate and just loosely cover with aluminum foil as well.
Also, a friend of mine who makes quarts of starters in advance with his pressure cooker weaned me away from making starters in the 1.040 range and closer to the 1.020 range. He provided me the info that basically boiled down to the fact that I am trying to get the yeast simply to reproduce, not make excessive alcohol.
However, after getting the smack pack/tube started with a low gravity starter, I will increase it with a second feeding of a higher OG starter. While I once heard I should try to match the gravity to be close to the end brew, I now am confortable just making the second round about 1.040, even if it is for a barley wine, tripple or other high gravity brew.