I'm a Lastpass convert.
I used to use 1Password, but was also frustrated with the lack of cross platform support (this was 1-2 years ago). This led me to try Lastpass, which has become the most important software/service I have ever used. It functions on every platform in a consistent manner (for instance, it offers to autofill on every platform, as opposed to just offering autofill on Macs but making me copy/paste things from one place to another when in windows). It also supports every browser via superb plugins, and has so many configuration and security options to satisfy even those people like me that are extreme security conscious.
For those people that are concerned about storing your sensitive data in the cloud (even though it is always encrypted locally before ever leaving your computer), keep in mind that if you are using 1password anywhere, or are syncing your 1password data with Dropbox, then you are already keeping your sensitive data in the cloud just like Lastpass.
What I especially like about Lastpass is the option for dual factor authentication. For instance, I have one trusted computer, which I have setup so I can access my Lastpass data with one strong password I have memorized. However, on any other computer, you would need my strong password PLUS a second form of authentication before you could access my data. In this case, I use a Yubikey, but Lastpass offers a couple of options for second factor authentication. I find this very secure even though my data is stored in the cloud. If someone could somehow get access to my data from the Lastpass servers, they wouldn't be able decrypt it without my strong password AND the physical key that I keep on me.
I rarely comment about any software or services, but I make the exception for Lastpass, because it really has become essential for me.