I'd think Tuesday would be the best day, but it looks like Friday mornings result in the highest open rates, though surprisingly enough, Saturday and Sunday seem to fare rather well.
I'm not validating any science behind these links, but it's interesting reading, so use this information as you will.
eROI Inc., Q2'06 eROI Email Statistics
What is the Best Time to Send an Email Promotion or Newsletter?
Friday Best Day For Email Newsletter Open Rates?
My .02? If it's unsolicited, the title's too sp@mmy and the message isn't specifically targeted to the intended recipient, it'll hit the trash bin before it ever gets opened.
BTW MJ, I'm famous too! LOL