Originally posted by ManAnt:

The crypts and such are not always in the same place, Regardless of the seed you reuse. Rock formations and building placements also often are off from where they was when previously created..

Originally posted by umop-apisdn:

In my experience, using the same seed on two different days will result in slightly different results; it would appear the world generation is only semi-deterministic.

Its based on patches (afaik). Big patches change terrain generation. Small ones that include fixes to spawn locations etc will re-roll the objects on map, others will not.

So there can be long periods with maps not changing at all, depending on frequency and specific details of given patch. We just dont have good enough patch logs to be sure at a glance.

Part of the problem is that the maps are designed to be compatibile across multiple patches, so the generation can change mid play, and its unnoticable till you make another world.