Buggy and loses data! Rated 2 out of 5 stars
I'm using Lightning 1.0 beta5 which is very buggy and so was the previous version. Lightning locks your calendars randomly which results in you losing your data, you have to remember to copy your data to the clipboard just in case this happens! When it does you have to restart Thunderbird and then right click on the locked calendar to unlock it. Pop-up reminders won't dismiss properly and stay on the screen when you change the reminder time and save the event for later. It needs a lot of work to make it stable, good idea though.
Just happened again! Got the dreaded Lightning error box: "An error occurred when writing to the calendar Lightning!" > Details... Error code: MODIFICATION_FAILED, Description: <empty>.
Lost my data again! Checked the website and this bug, or similar bugs, have been around for years - still not fixed?!?