An interesting video explaining a couple of the mapping techniques involved in making maps for HL2. Pretty complicated shiat, and sounds almost like modelling more than mapping. But still, shows just how friggen cool the engine is.

http://www.downloads-arena.com/file.asp?s=11037

Hehe, don't you remember every one yelling that mapping will be modeling in hl2 way before the e3 movie was out?