"...decline of ubuntu"
Ubuntu is not going away anytime soon, and please consider that Mint 9 LTS (version off ubuntu 10.4) will be around this website until April 2013....
Ubuntu presently has way too huge of an established user base, and you can easily google most any ubuntu topic on the web for an immediate answer.
Yes, Mint Debian, may and could win over linux users...but only after a lot more of what have been previously termed "rough edges" are smoothed out. But trying to google some debian lenny and/or squeeze topics for similar answers like you're use to seeing with ubuntu is a night-and-day difference.
There are some who will say that their grandmother/grandchildren run Mint Debian. To that,I say GREAT! FANTASTIC! But, to what applications does that grandma/grandson run in Debian? We'll never really know.
MINT presently has captured a niche market, and are obviously trying to break out of "niche" and go more mainstream with their new product/s to expand their user base. They absolutely do not want to stay only as a niche distro. They'll die in the market if they just stay the same.
It takes a lot of time, resources, and energy,(and luck to some extent), to increase market share. They work very diligently to attaining this end. If they grow the distro a minimum of 7% per year, every year, they'll be around for a long time.
I wish them success in their endeavor.