If you want to learn how perlin synthesis works, please have a look at:
The man himself, Ken Perlin, has some excellent demos of perlin noise on his website, including procedural terrain generation. Another example of terrain synthesis using perlin noise is Stephen Schmitt's marvellous World-Machine.
The perlin algorithm in L3DT is a bog-standard implementation, and doesn't yet feature any of the nice ridged multi-perlin options you might find elsewhere. It is, however, capable of making maps as large as 128k × 128k pixels using the mosaic map architecture.