For more than a year I ran various versions of Lightning and found it ok.
However when I upgraded to Thunderbird 3 I decided to see how I would get on using just Google calendar directly. I use gmail but find using thunderbird via ical as the best way to manage email for me, even though direct access to gmail via the web or my phone is useful too. So it had seemed natural to use Lightning to manage a google calendar in the same way, but I thought I would try using google calendar directly to see how I found it.
Several months later I don't think I will go back. It seems odd in a way to have Thunderbird and the browser (for calendar) both sat there side-by-side with no integration except for copy and paste, but I actually find it works better. As the article says, google calendar is fast, the natural language event adding is great, I can access it anywhere and searching works well. It's a good combination for me.