I would not do it.....

[jimgeo]

I would not keep your cover open because this is what Apple says:
Warning:
Always shut down the computer before opening it to avoid damaging its
internal components or the components you are installing. Do not open the computer
or attempt to install items inside it while it is on.
I have a Power Mac G5, i ran it with the cover open once, and then it just randomly got slower. I dusted it, and it got a little faster. I really don't think their is a problem with running it with the cover open, but I don't do it because Apple says not to.

 

[Peter.Cort]

well if you're going to install new components you should always shut it off, that's basic electronics. And I've never had an issue with running any of my pc's open and having them run slower, it might just be the placebo effect because whether or not it's open won't effect how it runs.

 

[aspire]

Thanks for a good laugh,

My computer hasn't had the side panel on for months, a couple well placed fans hanging around the inside have been helping keep it cool.