It's a great selection, and it's organized real nicely. You can enter some text, look through a ton of fonts, test them out in different ways, even see how they'll look together.
The fonts are high-quality. Some of them are kind of stupid, but none of them are garbage or glitchy.
Watch out: get too many fonts added to your collection and it may crash, and then you're back to square one. You can "back up" your collection as you go using your Copy and Paste with the Bookmark Collection feature. The feature is also useful for sending someone your list as a link. What a boon for client relations!
The fonts get served up fast when you embed them. And they make it easy to do it in a few different ways, to suit the need.
The thing I hate most about the whole thing is having to see the sentence "Grumpy wizards make toxic brew for the evil Queen and Jack" instead of just the alphabet, as a demo sentence, but it's good to be prodded into pasting in my own sentence.
So, once again, Google dominates because they made it (somewhat) usable, they didn't get ahead of themselves, and they didn't try to over-stylize a tool, like Typekit did. They made it easy to download the fonts. They basically found out what designers needed. I'd say, other than the instability, the biggest failing is that they anticipated the process of font selection too closely.
