Since I last wrote about Lightning things have really moved along.
Recently we saw the release of Lightning 0.7 for Thunderbird - this is a significant step towards matching, then beating outlook.
I can't seem to find a screenshot, but most of the rough edges which existed in the previous release have disappeared, the UI seems polished, and the experience while using it is... pleasing.
So if you want to try this but can't really find an excuse to do so, why don't you use thunderbird + imap + gmail, and then add your google calendar too. Try it for a week, and blog about how you got on.