I won't talk so much about the content of Google I/O, as your mileage may vary depending on what your area of focus is.
I will say this though - this is the best run conference that I have ever attended. I was able to check in and get my t-shirt in about 5 minutes, despite the fact that there were 4K other attendees, most of which were arriving right when I did. The food was great and free beverages and snacks were abundant, the wifi held up, the audio and visual quality was top notch, and you leave this conference with the feeling that Google is Great and Good, and Loves Us All Very Much.
The fact that they gave everyone a $200 T-Mobile Android G-2 didn't hurt either.