Hi, I read on GSMArena it's 8 Hours pertaining to the very first charge with a link atached. I use my Jawbone wall charger with the phone original cable. If you use a dock and sleep it's fully charged when you wake up.
Longer cables and PC might likely be unsatisfying. All the mobo makers like Asus, Gigabyte etc. now offer integrated chips that can charge smartphones through USB.
"...your battery is "charged" and it doesn't charge anymore while sitting in the charger, but after about an hour or two, in the non-charging state, the battery will drain a little and can immediately activate a full charge again if it is sitting in your charger. This "fast charge, slow discharge" process happens a few times during your 8 hours"..."If you use it after the 8 hours charge cycle, the battery is optimized and will stay in that condition for a long time before it starts its normal degrading."
(source: http://wiki.answers.com/Q/Does_the_iPhone_need_to_charge_8_hours_when_first_use )
