This afternoon we pushed a change live which got rid of the last remaining HTML validation error on the Australian IT homepage. When I joined News Digital Media in 2006, Aus IT was a creaky old table-based website, with so many validation errors we simply didn't run the validator over it (there was no useful information to be gained).
While validation may seem like a pretty basic thing, in a corporate environment it can be surprisingly difficult to achieve. It's taken people from several teams and some timely support from our product manager to get here.
This is only a step, since it's only one of our many sites and even then only the homepage so far. But it's a proof of concept and it put a big ol' smile on my face :D