I have collected a number of ascii-tabs (e-bass and guitar) during the last years. Plus a bunch of exercises and small snippets. In order to make them more readable, transposable, etc. I have written a little tool to convert them to Lilypond input.
It can run in batch mode, reads about 95% of my tabs without any problem and I get the midi output for free. If the tabs have an additional "rythmline" holding the time values, this in included in the conversion.