Notification Center in OS X Mavericks has an awesome new feature that lets you subscribe to updates from your favorite websites so they'll feed right into Notification Center. For websites that support it, I've found it to actually be extremely convenient. Here's how to get started:
Before starting, note that a website must support updates before you can actually use them. At this time, I don't know many that do but the number should grow as sites start integrating support for the feature. For this example, I'm using eBay.
That's all there is to it. While there seems to be very limited support for this right now, it's one of my favorite features of OS X Mavericks and I really hope other services start supporting it soon. I've found it especially useful if you sell a lot of items on eBay and want to keep up with messages and other interactions without having to check emails or launch web browsers.
If you've had a chance to try out website notifications in Mavericks as well, let us know what you think about them in the comments! And of course, if you've found sites that support them, by all means let us know what ones you've found!