10.04 to 12.04?

[Jens Kjaerulff]

I am thinking of upgrading from 10.04 to 12.04, just a click away in
the software centre (no particular reason other than to benefit from
recent fixes and continued support).

There are probably no easy answers (though I'd like some brief ones),
but I wonder how common soft/hardware in/compatibility related problems
are, resulting from such an upgrade?

Also, I am assuming all custom configurations will remain unchanged
after such an upgrade (default email and custom settings, www browser
bookmarks, various .rc files, repository settings for auto upgrades of
unsupported software, and such), please correct me if should not assume
so.