i'd love to see an attachment of some sort that you can install onto a bike and can produce an output able to recharge laptops and cell phones. i couldn't find anything with this capability based on a quick search.
For a manpower bike, I think it would be terrifically underpowered or terrifically difficult. As mentioned in a link from Luc, http://www.ski-epic.com/amsterdam_bicycles/, even the little headlights you stick on and power with the tires make cycling _much_ harder and produce very little light.
Charging a laptop/cell off of that would be... a challenge. =P
Borrowing energy from the battery of an electric bike would be a different story, but not all that helpful. Potentially useful if you stop at a coffee shop or something on your commute, but other than that, I can't see what it would do for you.
I researched this a while back because of an ingenious idea to decouple power and pedalling speed by putting a pedalled generator, a supercap, and an electric motor on a bicycle frame. Sadly, it would've been about 2x as heavy as a normal electric bicycle, and 60% as efficient.