I'm sure the X360 will break all records out of the gate. Launches have been getting bigger and bigger for years.
When the Playstation launched, it broke all records with 100,000 units sold in less than a week. Now, that would be a dismal failure.
I bet X360 hits two million (US) before Christmas without breaking a sweat, which will be a new record. It's hard to judge whether that's great or just good, though, with no competition in the market and launches becoming such a big deal (we even get software launch parties and media coverage now--like Madden this year, or Halo last year).