In my time of using it, I've found LastPass to be very intuitive once it's up and installed. During the install, LastPass will scan your browsers for saved passwords and show them to you (prepare to be shocked at how easy it is for an application to see your browser passwords!). You can then choose to migrate these passwords to the LastPass database, which is what I did. After installation, LastPass will disable Firefox's built-in insecure password manager and set itself as the default password manager, watching for any new password entries and asking you if you want to save the details to the database.
It will also import your password data from multiple sources, including KeePass, RoboForm, Password Safe and so on. I successfully imported my password database from KeePass and migrated it to LastPass. Impressive!
I tried multiple-PC synchronization between my desktop running Mozilla Firefox and Windows XP, and my laptop running Mozilla Firefox and a dualboot configuration of Windows 7 RC and Gentoo Linux. Apart from having to install and setup the software multiple times, the synchronization was a breeze and worked well between browsers, computers and operating systems. The thing that pleased me most was that the unencrypted database never leaves your computers. Any and all synchronization happens with an encrypted file across computers.
The web-interface is full of AJAX which might look cool but is inherently useless on old browsers which might not support the browser plugin. This is one thing which I'm not too happy with, since I sometimes have to browse the Internet on a command-line interface with lynx. LastPass people, please take notice!