Ubuntu took off from heavy advertising. Advertising and marketing works, and the initial "get as many free disks as you want " shipit deal helped there as well.
Now, what they failed to do is capitalize on this advertising. They should immediately (as soon as they saw they had a hit on their hands) have gone to selling their own machines. Relying on dell. some *mart, some online mom and pop store, etc is not the same.
They don't need every hardware config under the sun, just maybe six machines total, don't go crazy there. This needs to be like an Apple effort, just using open source, integrated hardware and software in nice packages.
They need a netbook (go for ARM, make the breakthrough), a full laptop with optical drive, an entry level cheapish desktop, a higher end workstation/gaming type desktop, expensive but all top shelf components, don't be scared, just do it, a SOHO tower server perhaps that comes with NAS, then a rackmount enterprise server.
They use the LTS releases as the target OS for those machines. The main hired on devs use those machines all the time, so they really grok how to make them fly and get rock solid.
Now, the support is two tier, you own a bonafide branded Ubuntu machine, you get first tier support. Everyone else gets second tier (which is what Ubuntu has now, pure anarchy with hardware, good luck if it works or not, go wade through the forums pages deep with "help me plz").
first tier, separate forum, and the devs, or other offical hired on dudes, DO read the forums there and respond. And quickly. You take the people's money, you answer their questions and fix problems as fast as possible.
First tier branded machines get the REAL "just works" treatment. The rest is like now, good luck with your hardware, might work, might not, go haunt the second tier forums, see what needs to be done there. If you want the every six month bleeding edge releases, oh well, good luck. sure you can run it..but don't expect the same support as they give people who have paid for the hardware and software. Hardware they sell should stay supported for two LTS cycles. That's more than enough now a days for people to milk their hardware out. Chances are, if the hardware and software was really a good match, it would work longer than that, but officially, make it two cycles.
And they should be able to keep cost competitive in this, as they have the resources for economies of scale and some good Q&A before making hardware selection for the branded machines. If local mom and pops can assemble and sell generic machines, so can a big company like Canonical.
Every new LTS release, new hardware comes out, and it "just works", everything, wireless, all of it.
*Most* people don't give a rat's ass about upgrading their OS and machines every six months, look how many people and businesses are still running XP and some older hardware. They want "just works" and "finally, I got this freekin SOB computer figured out and can use it now" over bleeding edge every other week something new is added/updated, and something old that worked, stops working. That gets way annoying to the other 99% of the humans out there who aren't serious devs/hobbiests. Real annoying.
You want linux mainstream on the desktop, or you want to keep it for hardcore nerds only, choose one.