I would on the following conditions (some of which are optional if others can't be met):
1st: I want to be paid for doing so. I think that is more than fair.
2nd: I find artificial insemination bland and sterile. So I would gladly do it for free if I can make a "direct deposit" *wink*
3rd: If option 2 can't be met, I want all my donations to be genetically enhanced with super-human DNA. I'm sure there is some mad scientist waiting to try some experimental procedure. Let him have some fun.
4th: If options 2 or 3 can't be met, then... in addition to payment, I also want Season 5-current of House M.D. DVDs (this means that if the series continues, I'm still being given additional seasons of DVDs as they're released).
5th: If options 2, 3, or 4 can't be met (then god help us all), I want the payment mentioned in option 1 to be the sum total of one million dollars.
If options 2 - 5 are considered unreasonable or undo-able, then I supposed I'm not fit donor material.