I had to do this once, with the added fun of arbitrarily complex processing of the log lines. I used POE::Wheel::FollowTail http://search.cpan.org/dist/POE/lib/POE/Wheel/FollowTail.pm which worked a treat. Probably overkill, but it opens a whole world of event based log processing fun to you. I handled some busy weblogs and as well as looking for errors, produced a pile of stats every minute too

Cheers,
R.