Currently it is at 3,000, which is very easy to hit when you are making megafarms and big builds/structures and whatnot. When you hit the limit, you are forced to try and cram all of your stuff into a column, which is really just not fun, and often not feasible. The limit should really be more like 10,000, because with that size you can have enough room to fit plenty of mega-farms, while also having enough leftover for things like bridges and builds.