last year my site was taken down on qwk.net because this plugin used so many resoucres on the cpu it unstabilized the server for all the shared hosted sites. so the server people took my site offline. this happened whenever we would receive an increase in hits to our site.
today again, our site was taken down by site5 (new hosts) because the mailchimp server had runaway php scripts that used too many resources on the site and made the server unstable for the other users.
i have raised this issue with mailchimp, but they say there are not any problems. i have disabled the plugin--and no more problems.
so i give a warning to people using wordpress with multiple blogs, this plugin could cause your site to be taken offline by your hosting company as happens repeatedly with me over the last year.