There's a new web service launched every day it seems. In fact, Yahoo!, Google, and Microsoft are each launching new web services almost daily, certainly at least weekly.
So it's hard to keep track of all of them. But we try and services like TechCrunch help a lot.
In order to understand all of these services, you have to actually use them and that's pretty time consuming.
You can go there, sign up, and start riffing. You'll also benefit from all the riffing that others are doing via Riffs' recommendation engine.
The cool thing about Riffs is that they've loaded in a huge database of stuff that you might like to riff on; music, books, gadgets, restaurants, events, travel destinations, cars, etc. So you don't have to load in the item to riff on it. But if you do want to load in the item, you can post with a bookmarket like delicious.
I've been riffing this morning and I've added a Riff Roll to my blog on the lower right, below my Flickr bagde. As I riff, you'll see my raves.
It will be interesting to watch and see what develops as more people use it.