Mailing List

This morning Google presented us with a PR4!  And, a recent post made its way across the internet universe so our numbers have jumped.  That said, we're contemplating a monthly newsletter.

What magic number should you hit before starting a mailing list?  What percentage of your readers actually roll over into mailing subscribers?  Successes?  Failures?  Great mailing list service -- or ones that we should steer clear of?

Thanks so much for any feedback,
Lane