This article is all over the internets today! My sweetie used to suffer from some form of mild hyponatremia after long group rides, which we discovered when stoking him up with salty food (ramen noodles!) after such rides staved off his tendency to have low-blood-pressure dizziness and near-fainting.

But personally I don't think I'm at risk! According to http://cptips.com/fluids.htm we should take 4 to 8 oz every 15 minutes. On a hard ride I don't have time to drink, and I end up going through barely 18 oz in 2 hours! I don't guzzle when I get home either, it takes me something like an hour after I'm off the bike to realize I haven't peed and my mouth is like cotton and that when I sip water it tastes like the sweetest elixir.

That site also has great info about treading the line between hydration and hyponatremia, and discusses the relevance of electrolyte replacement and glucose-containing drinks.