Yahoo answers has this to say:
According to the many media experts I snagged for this question, Tuesdays are the most promising days for home-entertainment industries to release, say, 13 shiny new tracks from Toby Keith. Tuesdays are also the easiest days for data crunchers to begin tracking weekly sales of said stuff.
"It's quite simple, actually," states Mark Berman, of the trade magazine MediaWeek. "Since Monday is the day after the weekend, consumers are not at their height of awareness. And because Friday is the day before the weekend, consumers are preoccupied with other things. That leaves Tuesday, Wednesday and Thursday. Since Tuesday comes first, it leaves Wednesday and Thursday open to actually buy [and track sales of] the product. So, Tuesday it is!"
Full linkage here:
http://answers.yahoo.com/question/index?qid=20080128124656AAFn3u4