Re: Thunderbird + Lightning
Freeware type Office copies might work for small business and home users, but for the vast majority of enterprise users, it's simply not up to the job. Especially Excel.
Anecdotal though it may be I've never had a need that Calc wasn't more than up to. Though, to be fair, I mostly use spreadsheets as a place to dump database queries to so that I can easily give them to someone else. Someone else does all the book keeping and accounting that is Excel's strong point.
As for Thunderbird + Lightning, on that I have to say it's just not up to the job even for my relatively modest needs. I've been there and tried that. After a couple months of frustration I gave up and went back to Outlook. GMail Enterprise can do the job, but it brings in its own headaches. The biggest one for us is that there are no bulk tools except an import. If you need to change a huge batch of accounts you have to touch every single one of them.
For most businesses that wouldn't be a problem, but we were using them for student email accounts. That meant every June some lucky sod got to go in and delete 600 email accounts for outgoing students one at a time over a not-especially-fast web based interface. Even worse, every time the suits (AKA the guys with PHDs in education who can't find Outlook if you delete the shortcut from the desktop) decided something about those accounts needed to change we had to touch every single one of them, which took about 3 days of mind numbing click-click-click. I could see GMail as an alternative in a more normal enterprise, but it doesn't cut it for us.