I nod. period. I nod at BMX kids, I nod at commuters, I nod to snobs, I not to freds, I nod at cagers and even dogs and cats. Waving is too much work, I have hills to climb.

Seriously, If you miss the chance to wave, or nod at another cyclist, dont worry about it. I have been so focused on making it home, or about hitting a green light, I have totaly blown off other cyclists that have waved to me. I'm sure they have done the same, i think most will forget about it within a few minutes.