Depends on whether you're trying to fit with how things tend to be done by larger groups, or whether you're going against the grain. For many industries, Tuesday is the day of the week when everything 'new' releases. This is likely because that way physical stuff has a chance to get to stores, be set up, etc.
On the other hand, since most of us are dealing with digital sales and / or POD books we don't have to worry about that. I'm not sure whether it would be better to swim in the stream with everyone else, or whether releasing on a different day might provide an advantage. I have seen a few products, in different areas of entertainment, release on unique dates. (I think "Beatles Rock Band" did that a few years back; I seem to recall having to go out an odd day to get it.)
One thing I *will* say is this: Check what else is releasing the day you pick!! I just found out that a book with some similarities to what I've written is releasing the day I chose. *head, meet desk* (Enough that I don't know if I wanna release the same day; not enough that anyone would think my book is a clone, thank God.)
I think this is something that might matter tremendously to some people, and that may matter very little to others. In the end, the real thing of importance is ensuring you have a quality book with an eye catching cover and a blurb that will both grab readers' attention and be true to what's actually between the covers.
Good luck!