To Dos aren't stored on the server, so they don't sync by themselves. But you can embed To Dos within Notes and sync them that way. All of this may take a while to get your head around, but after using them for a few days, I am already starting to wonder what I did without them.
Smart Mailboxes have also been beefed up. You can now make a new Smart Mailbox by right-clicking on an existing one, selecting Duplicate and editing it from there. Smart Mailboxes are also quicker at gathering data than they were in Tiger, repeating a theme that carries over elsewhere in Leopard: Old functions and new are snappier.
One of the biggest additions to Mail from an aesthetic standpoint is the Stationery tab. When creating a new e-mail, clicking the Show Stationery button in the upper right presents a menu full of designs that range from birthday cards to photo templates to fun notes. You can also browse your iPhoto Library for images to drop into your e-mail or stationery template by clicking the new Photo Browser button.
The downside to using Stationery, of course, is that it inevitably increases the size of a message -- e-mails that would be only a few kilobytes in size as text can easily get several times larger once you add graphics and photos. But if tools become available for creating third-party stationery or corporate identity templates, this may well become a huge sleeper feature.
You are now also able to create Archives of POP3 accounts by right-clicking on the mailbox. While a lot of people will be using Leopard's Time Machine backup feature, it sure feels better to have a fully portable copy of your e-mail account in .mbox format.
Archives don't appear to be compressed -- in my testing, their file sizes have corresponded with the original mailbox size -- but you can always compress the Archive after exporting.
Although there are a lot of really cool features in Mail, the coolest might be the "data detectors." If you get an e-mail with a signature or a date included, you can mouse over it and see a bit of Apple magic: A triangle will appear, offering a drop-down menu that indicates information that can be imported into Address Book contact or iCal.
While the feature isn't 100% perfect, it really cuts down on data entry time and works so intuitively that, within days, you will automatically be looking for data detectors within your messages. The amount of extra information that you can easily gather from your e-mails will skyrocket.
Apple has truly taken e-mail to a higher level with Leopard Mail. While the list of new features is impressive, the implementation is what blows my socks off. Everything is so intuitive that it barely takes any learning, yet I am using Mail in a completely different, more productive and fun way. Kudos, Apple.
iCal
iCal gets a big design overhaul, but like a lot of other things in Leopard, there's nothing that will confuse or distract people from the task at hand.
The first thing you'll notice is that it's done away with the brushed metal look and adopted the smooth gray look and feel that characterizes Leopard. The bottom of the left nav bar now has a more legible monthly calendar with much bigger numbers. The Day/Week/Month View buttons as well as the search window have moved from the bottom to the top in Leopard, making them more visible and useful.
The left nav bar still lists your Calendars, but now also includes the IMAP e-mail accounts where you store your To Dos. The pushpin button brings up your To Do list, as it did in the previous version, but now the To Dos created in Mail are part of the list.
You can reprioritize them and close them from here, or move them into other calendars. In the publishing field, you can now also publish your To Dos to your .Mac or other Webdav calendar.