Since the 1.3 update, many mods broke. A lot of them have been updated (MCedit), but one in particular, "Single Player Commands", has not, which has brought my progress on the map to a temporary halt :( . I can still build certain things...but definitely not at the same speed as before, which is frustrating. I will be putting any major sections of the map on hold until "Single Player Commands" is up and running again.
Let's hope for a quick update!
PS, This is in no way directed at the mod creators. I don't expect all mods developed freely by the community to be 100% working on patch day. Thank you all for your tireless efforts to make MineCraft more enjoyable!