Aside from the arbitrary relocation of the window controls this seems to be a stable release with lots of great improvements (especially if you are coming from 9.04 rather than 9.10, which included the early stages of some of these improvements).
Fenixp: ... ... Seriously, is there any reason whatsoever to do THAT?
No adequate reason has been given from what I've seen. I'm not sure that even the designers know their own reasons. In the words of
one of the designers behind this decision, "Is it better or worse? It is quite hard to tell." I wish I was making this up.
This change has huge ramifications for Linux development, because this customisation only automatically applies to software using the native windowing system (metacity/compiz); programs that a different windowing system--and there are a lot in that category--do not inherit this preference and will continue to have the buttons on the right-hand side until their designers add specific support for this new behaviour. There will also be an expectation for the projects Ubuntu builds upon--such as Gnome--to implement support for this preference in their programs.
Also of significance is that this change is for the "LTS" (long-term support) branch, which is widely deployed by companies that want a reliable, regularly-patched version that will remain compatible with their existing software. Ubuntu 10 is compatible with software, oh yes, but not with the actual users.
If I was a primary Ubuntu user who didn't already know about this I would be really, really ticked off at the end of the upgrade process. The upgrade window presented to 9.x users warns about all sorts of potential issues, but not this.