The fact is if all you want to do is download a large file overnight or play music, there is no need to have the lid open and the display showing (your Mac will not overheat by doing a simple task like this). It all depends how much CPU is actually being used, so if you aren't using a lot of processing power then it should not overheat. Too bad the new MacBook Air doesn't solve the issue either.
Here are some suggestions:
A Free Utility you can start with is InsomniaX, which has the ability to toggle disable/enable sleep mode . I checked on the developers site and there is credible information that since 2006 it has worked for many , and a quote from a user here gives relief if you have the latest MacBook.
No damage received to my new MBP 2.6ghz/4GB RAM/250 5400RPM hard drive laptop.
Although it can get hot when it’s open playing WoW or converting movie files, when i leave it closed to say, download a torrent over night, and set the fans to 3000rpm, I usually wake up to the temp. output of InsomniaX being somewhere near 109-115. Which is pretty good, becuase this laptop normally runs around 115-130 in normal use with Safari and/or itunes and a couple other programs running.
Another Utility is Sleepless (not free), which allows you to do the following:
· Can disable sleep with lid closed of course
· Safe Sleep (Hibernate) with one click
· One click activation / deactivation
· Menu icon with commands menu
· No processor time waste
Are you thinking about dual booting your Mac with Windows? If your curious about it I have posted a recent article on the steps to do so here.
Hopefully these suggestions if used properly can help your usage of your Mac even better now, just keep in mind that you are accepting responsibility of disabling a built in Mac feature and its possible consequences.