If you have a large number of people to check for, and you then run an on:Connect to run a whois if the nick is online... you may end up flooding yourself off.
You could intercept the /notify reply instead. Have notify check on join. I don't see it mentioned much, but on some networks (like DALnet), you can actually get the user's host from the /notify reply - meaning you don't need to use /ison or /whois at all
PastMaster
