Monday theres too much going on. Friday nobody cares because it's the start of the weekend. Tues/Weds gives you time to deal with bugs and problems that crop up after millions of users flood your site after the announcement.
Consider for example making a submission to reddit or digg. When would be a good time to do so to maximize the expected number of people who will check it out?
At this point, Digg and Reddit are hard to use unless you game them. It's so random as to whether it gets dugg/buried or up'd/down'd at the beginning. I hope you have a lot of friends with the right accounts or a way of paying $1/Digg.
Agreed for sites like reddit, digg, maybe even closer to 330 or 4am on Sunday. None of the usual, intelligent users are on at that time to be critical of your site or discredit the comments you leave. Everyone is just blindly voting.
Of course, press releases are probably the most reliable and effective way.
I'm going to guess that Monday is the worst, because people are miserable they just got into work, as well as swamped with additional work that came about over the weekend. Friday sucks because people want to go home and be done with that week. Few people work on the weekend. Tuesday is best because it must give a person four business days for followup. Any reporter/businessperson/client who wants to reach the company has time to do so over the next few days. That would be my guess.
I've noticed weekends are nice because few folks are launching--and bloggers are more chill and likely to review your submission. Just a general thing I've noticed.
With that said, we launched Monday afternoon. Made to digg frontpage Tuesday evening; TechCrunch on Thursday 4-5am EST.
If you want to get your stuff on a social news site you'd better start making friends now. A disproportionate numbers of diggs on the front page come from a small percentage of users.
I realize that the middle of the week has the highest internet traffic. But high traffic might result in your submission being swamped by other people's submissions.
Monday theres too much going on. Friday nobody cares because it's the start of the weekend. Tues/Weds gives you time to deal with bugs and problems that crop up after millions of users flood your site after the announcement.