Logs are stored on Mibbit's servers so you can access/search them from any computer as long as you are logged into your account. Viewing your logs and/or downloading is pretty much beta at the moment. Downloading too many lines (as .zip file) results in a server error (work in progress). See also http://blog.mibbit.com/?p=911
You must be logged onto the main client and have the preference enabled for logging to occur. Logs are private; we don't access them or give them to other people.