Demiron of the US-Elune server bought forth a concern about the new achievement system on the official forums recently: How does a World Explorer get all the world explored, especially the enemy faction capitals and cities?
I'd like to assure Demiron and people like him that it really is possible. Alex even wrote a nice handy mini-guide to sneaking into the cities to get Crown of the Fire Festival which should work for exploring too. If you're not a stealth class, it can be harder, but knowing the location of a few back doors and having an epic mount speedy enough to outrun guards can help a lot in those cases.
One other concern for a World Explorer, though, is figuring out exactly where they have and haven't been, and for that, Bornakk did drop a nice little hint in the thread: There will be a way to see which places you haven't explored so that you know where to go to get that shiny new achievement ding.
More help for achievements is certainly a good thing, and should help those of us scatterbrained enough that we can't quite remember if we covered every square inch of Stranglethorn or not. Hopefully, this type of help can extend to other achievements as well, so you don't have to figure out whether you have 500 daily quests to go for that achievement, or only 50.