I have had a look through the new halflife.fgd apr 15 2003 - 3.1.0.0 - updated with studio() references to enable model display in 3D view.
You can use this .fgd with Hammer 3.4 if you don't want to try out the new Beta. Things that might be of interest are the addition of .mdl choice to most of the monster and weapon entities, as well as a few new entities commonly found other Mod .fgd's. It makes placing models easier, but you won't be able to see them in the 3D view unless you use the Hammer 3.5.
All news so far is that the New 3.5 is excellent and should make mapping easier. I will update the TWHL HL entity guide soon (read after next uni assignment