Yes, this date has been mentioned before by Tom Bergeron, but it appears to be Official. According to the Orlando Sentinel - who I assume gets a ABC Press Release like every other media outlet:

ABC also announced that “Dancing With the Stars,” its most popular series, will start its 10th season on March 22. There will be a two-hour show that night, and a two-hour show March 29. The scores will be averaged from both shows, and the lowest-scoring team will be ejected March 30. (”Dancing” hosts Samantha Harris and Tom Bergeron are shown in this ABC photo by Bob D’Amico.)

The show will air at 8 p.m. Mondays and 8 p.m. Tuesdays — which means that “Dancing” will run against Fox’s “American Idol.” The latest celebrities will be announced later, ABC said.

No mention of the number of couples, and it *sounds* like only one couple will be eliminated in the second week. Also note the air times for both shows – the tuesday show normally starts at 9 pm eastern time, not 8. Direct competition with American Idol – hasn’t it always competed with AI on tuesdays? Or am I mis-remembering?

Granted our press corp are often sloppy about reporting and word selection, but the author of this blog says that scores from the first two mondays will be “averaged” – that’s a pretty big departure from the norm as well. Usually they’re just added together and the low score goes home. Things that make you go “hmmmm…”