Done it plenty of times myself.  Get one of those magnetic flexi cables, you can get them from auto stores, or use air to blow them out.  Have used both methods with success several times.

This is the sort of thing:

http://www.ebay.com.au/itm/Flexible-Rod-Magnetic-Tip-Tool-Flex-Pick-Up-Tools-3904-/400217760678?pt=Motors_Automotive_Tools&hash=item5d2ed663a6

Yep been there done that twice in the same job. Bloody amazing. It will drop out while you are riding. I sat my bike upright and started it. The nut fell out then. But lost one completely..... I use a towel underneath now. Once bitten twice shy

Yep it's frustrating, thanks KC, wil look into the magnet