I mentioned earlier that I've become a huge fan of Backpack. It is my home page in all of my browsers. I've been able to consolidate so many other random things into it. The reminder feature is stunningly useful. I'm still learning new ways to use it (mobile integration is the current item). I just can't say enough. However, the only issue with Backpack is if you happen to not be online, you are stuck. Here comes PackRat to the rescue. PackRat is a great Mac OS X application that connects to Backpack and gives you an offline version. You give it your Backpack username and API key, it connects and within seconds downloads all of your content to your laptop. You can then make changes offline and reconnect and magically it's all back on your Backpack site. It even allows you to manage reminders.
The spiffy thing about PackRat is that since it isn't running in a browser, there is some stuff that it does nicer than Backpack, like tag navigation. I'm finding myself using PackRat a decent amount even when I am online as it has a nearly identical user experience to Backpack and is a bit faster without the HTTP reloads in the middle.
If you are an avid Backpack user, and a Mac user, this is a great program to add. I just wish there was also a Windows version.