Firstly, this game sounds rad.
I first heard of Descent watching the great Shut Up and Sit Down special on it, and I decided I really wanted it about 10 minutes into the 30 minute video. Google swiftly revealed the coming of 2nd Ed, and I decided rather than splurge on something soon to be out of date, I would sit on my hands and wait for the update to come out before buying it. My friends all loved Mansions of Madness, which seemed to be essentially the Lovecraft version of Descent (that's probably wrong) so I thought it would go down really well with my group.
That was a few months ago.
Since then, my chums have started playing D&D4E (I worry about posting that name on the Internet for fear of bringing down the wrath of D&D fans. It's like saying Candyman 3 times in the mirror) and I am concerned that for them, Descent isn't going to provide a different enough experience to justify getting out on the table too often. On the other hand, the competitive aspect, as well as the mechanics, seem very different to D&D, and Mansions of Madness certainly complements Call of Cthulhu rather than competes with it. Does anyone play both? Do you think both can peacefully coexist or will one replace the other?