I started just replying with a "No thanks, but I'll hang onto your info in case anything changes or I come across anyone else who's looking", and then I add the

I started just replying with a "No thanks, but I'll hang onto your info in case anything changes or I come across anyone else who's looking", and then I add their email to a "recruiters" contact list in Gmail. I now have close to 300 folks split between internal/external/vc. I haven't needed to use the list yet, but I have shared it with one or two friends who were interested in changing jobs.