I'll echo the observation that thinner gauge 3/8" line still has an ok feel in the hand (to me at least). I've still got 7/16" for my sheet jib sheets. But the 3/8" line I most recently bought to replace the previous 1/2" for the mainsheet halyard feels just fine when I hoist the mainsail by hand all the way to the top.
I'm sure that I'll opt for 3/8" for my next jib sheet replacement. On keel boats, one generally doesn't pull jib sheets hard by hand. Instead, when tacking, the need is to pull by hand quickly only the slack as the sheet comes off the wraps already on the winch. Once the wind catches the jib, then its the winch handle and the friction of the line on the winch drum that does the rest of the tensioning.
Also today's lines have much higher breaking strength and lower stretch than they did a three decades ago when Hunter made their rigging specification for our Cherubini models. A mid-range 3/8" line today in 2010, probably has equal or better stretch/breaking characteristics than say a mid-range 1/2" line did in 1980.