I.Am-Half-Life has a few warnings up for folks updating their half-Life to version 1.0.1.3, these two seem worth passing along:

• The update will overwrite your TFC autoexec.cfg file, so be sure to keep a backup of Half-Life/tfc/autoexec.cfg to avoid having to re-create all of your binds, aliases, and scripts. Your Half-Life/valve/autoexec.cfg and any TFC map- and class-specific configs (spy.cfg, 2fort.cfg, etc.) should be safe, but I'd back them up too just to be sure.
• Demos recorded under previous versions cannot be played back by the Half-Life v1.0.1.3. Attempts to play old demos will give an error message similar to: ERROR: demo protocol outdated, Demo file protocols 38N:4D, Server protocol is at 39N:D. I hope whatever "Demo playback fixed" means is worth the hassle :)