Google Font API allows makers of web pages to use non-standard web fonts to apparently 'make the web beautiful'. Related IxD posts discuss the creative aspect of using a font. However, if you look at the type faces google is offering they look like rats have chewed on the letters even at larger type sizes. This is a usability issue since it makes the text so hard to read.
Fonts like Verdana and Georgia were designed for all the tiny light bulbs that make up a screen and really improve legibility.
Though I do like the technology, the quality is just not there. If you must use a custom font there are CSS techniques that will satisfy most accessibility and SEO requirements.