If you overhydrate, the experts say you can develop hyponaotremia, which definitely can kill you. They also say swelling of hands can be a symptom so it probably is a good thing to read up on. Here's an article that scared the **** out of me!

http://runningdoctor.runnersworld.com/2008/05/should-i-do-the.html

Len,

Do your hands never swell during marathons? 

I sweat a disproportionate amount compared to most people.  For instance, when I do a moderate to easy pace, 65 minute 7 mile run with temps in the 60s-70s I will loose from 5-7 pounds during the run.  This is everyday.  I don't drink anything during the fall and winter runs.  During the summer I'll drink about 20 ounces every 45 minutes when temps are in the high 80 and above. 

Slowpokechu:

My hands usually do swell a little.  My ring gets tight.  I try to remember to relax.  On downhill portions of the marathon I will let my arms swing loose a bit to help loosen things up.  If I think about it I also will put my hands over my head for a few seconds during water breaks.  I drink a cup electrolyte at every water stop, except maybe mile 25.  I also take either honey packets every 2-4 miles or the equivalent of a jelly bean every mile for energy.

I haven't taken salt during a race yet but it is something that I am considering.