edit: It looks like they've got the same situation vis-a-vis ads as all Kindles - yes they have ads, there is some attempt to make them unobtrusive, and they only have ads in the US.
http://www.zdnet.com/article/all-kindle-fire-hd-models-ad-su...
So that explains that. Now to find out how hard flashing a new OS would be. :)
Also note that the HD 6 and HD 7 are still not flashable, and they've been out for some time. Amazon seems to have gone out of their way to make this a difficult device to tinker on.
My recommendation is to find a well-treated used Nexus 7 and you will have a much better time of things. They are much easier to flash with better ROM support. Please don't buy this thing with the expectation of enjoying some weekend tinkering - it's not worth your time.
(I suppose I'll caveat that the one scenario where it would make sense to get it now would be that v1 firmwares contain bugs that will make your life easier when exploits are found, but still - probably not worth it)
Its not some free magical data flying around on its own.