A few days ago i wanted to try getting Mozilla Thunderbird working with Microsoft Exchange. Sort of worked. I got the email working but I couldn't get global access list working (yes I tried the different ports, etc.).
Even if I had gotten it working there was still the calendar issue...
I used thunderbird for a few minutes and really missed Apple Mail's smart mailboxes. So I ended up dumping thunderbird altogether.
Basically if you need to connect to an exchange Server on OSX Outlook for Mac or Apple Mail is probably solution you will be happy with.
That got me thinking of different email clients to use on my MacBook pro at home. I only use pop3 for access so my needs are simpler. I used to use thunderbird for email back when I used Windows. My favorite Windows email client was Agent, which I see is up to v6 now.
All the fancy features I used in any email client were really for spam control and Popfile has taken care of that since 2003 or so. (BTW, if you get get any spam at all you aren't using Popfile). So I was looking a simpler email client. One of Leo Laporte's picks on a recent Macbreak weekly was Sparrow. It's in the App store. Tried the free version for 2 minutes before I registered it.
The iPhone version is easily the best way to do gmail on that platform. No iPad version yet, bit the iPhone version does the job there too.