I can't see any reason why that wouldn't work, although I would question
how efficient it would really be - the games are gigabytes in size, and
most of that is visual/audio content which will need to be loaded across
your network every time the game wants to load something, as opposed to
just loaded from your local HD into memory.

Even with a gigabit network, I suspect that this might increase your
loading times significantly, because you'll have the additional latency
of the network to factor in when data is being retrieved from its source
on the remote drive.

Nethertheless, its worth a try, but if it were me, I'd install and
seperately maintain 2 copies of steam and the games on each system -
perhaps only ever updating one via steam, and copying the steam game
content across the network if one of the .GCFs were given a
significantly large update
(a .GCF generally contains 95-98% of all game data, and, from what I've
seen is the only file which is modified when steam downloads updates for
a game)