I can start using this immediately for debugging the backend of a web application during development. For some kinds of debugging, it's preferable to log output to a file or tty instead of printing on the page during a request or stepping through a debugger. This is particularly true in frameworks where you might be trying to debug something that's happened after the rendering step.
I would typically use standard debug logging and tail the output in a terminal while I test, but having that output in a browser, searchable, filterable by RegExp adds a whole additional layer of ease of use. Showing this to all the backend devs on my team today!
less is great, and I'm certainly comfortable using it (nice snippet btw!). Other devs on my team who are more web focused would probably find rtail easier to use.
We also have a Vagrant box for each project, and rtail would be trivial to add to the Vagrant template so that every development box has this running on a specific port without any setup or fiddling needed by each developer. At least that's the direction I'm thinking of going in right now, without having actually tried it out. :)
