I think we're a few years too early - I'm just starting to look at video editing, and everything I've tried is half-baked and alpha-quality software. Assuming a powerful-enough machine, the only current option is VMWare plus Windows XP plus some commercial Windows software - or a second machine running Windows.

Does someone else know better and can indicate a usable, functional package for Linux?

See my comment on the "conversion" discussion.

Ogg Theora isn't a very good format to use for editing.

To paraphrase Obi-Wan Kanobi:

Use the source, Luke - use the source!

Or any format it can be converted to losslessly.

Then convert to the presentation format(s) after editing.

Too bad! I'll have to stick with my 'one take no edits' tutorial recording method via Istanbul.

What was the video shot in? How/why did it wind-up in Theora prior to editing?

Theora is a intended for low-bitrate delivery. Not editing. As such, encoding to Theora should be the last step you perform.

What was the video shot in? How/why did it wind-up in Theora prior to editing?

It was created with Istanbul Desktop Session Recorder. Output is immediate as Theora.

Can you fiddle with quality settings at all? You might want to set a high quality on your captures, and see if there is an option to force the use of only I frames. This will at least give you video that is more suitable for editing.

Even if an editor doesn't specifically support Theora as input, you might (depending on the design of the editor) be able to pipe the input through ffmpeg to convert.