Question: I am looking for a visual tail tool that can monitor several local or remote log files.

Optional features that interest me: color highlight based on log error level, coloring for special words, filtering of messages and/or notifications on new activity.

Answer: 
I found a tool that can do this [GeekTool](http://projects.tynsoe.org/en/geektool/), it even has a version that works on Lion (see the forum).

It can be used to do just simple tails, without filtering or other stuff, so maybe someone has a better alternative.
[PostRemoteLog](http://www.oriontransfer.co.nz/projects/admin-toolbox/post-remote-log/index) (free)
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PostRemoteLog has Growl notifications support and it is free.