No, this isn't THAT subject.

I have come across a bug which results in a merchant being unavailable and a quest unable to be completed. Apparently I can fix this by using the console to reset the quest.

I have played Skyrim unmodded for the last year but have finally started paying attention to some of the mods out there and a couple in particular are looking extremely attractive. The first is SkyrimUI and the second is a compilation of HD textures (both mods that I shouldn't have to get on a PC game released in 2011... ).

Both of these things have a common denominator. Despite the hundreds of hours I have put into Skyrim, there are a lot of Achievements I still have not gained, and even more now that I have Dawnguard and Hearthfire... and still more, presumably, when Dragonborn is released. As i recall, using the console and using mods locks out all future Achievements for that character file. Is this the case, or does it depend on the commands/mods being used?

Using the console only disables achievements for that specific play-session. Closing and restarting the game re enables achievements.

Most modifications done with the cosole (ie changing the value of a global variable) are saved with the game save, thus if you really think "achievements" are important, just save, quit and restart each time you use the console?