Mike Burns

Still an issue up to 1.7.9.
Tests done: Ran a utility that checks the world files for errors. None found. No large number of entities. No redstone circuits. Downloaded MCEdit and deleted chunks around where lag occured; did not fix issue (also ran that program's chunk verification utility to no avail; no errors found).
Created a fresh copy of the world using the same seed. No lag encountered in the lag locations.
Experimented with removing certain region files from around the lag areas from the world folder; in the end the issue was resolved. One of the region files must have been corrupted in some strange way, as the lag areas turned out to be right around the 4 corners of that region.
Maybe my issue isn't the same as everyone elses', but checking the areas in a fresh world and swapping out region files is worth a try.

I'm having this issue in 1.7.4 in SMP- extreme frame rate drops (to 0) in specific locations. Occurs in same locations for all clients. Console messages when debugging are similar to the console output shown above. I restored a backup of the entire world directory (from a point where this didn't occur) and the issue still occurred. I rolled back to 1.7.2 (clients and server) and the issue still occured.