When I promote an affiliate link through safelists, I usually track conversions by checking the stats on the site I'm promoting. Most affiliate programs give you click or referral data, so I keep an eye on that regularly.

I also monitor my referral count — if I see a jump after a mailing, that’s usually a good sign something worked.
It’s not always 100% accurate, but over time you can start spotting patterns: which subject lines bring the most clicks, which mailers perform better, and so on.

How do you track your results? Do you use tracking tools or just rely on built-in stats?