The problem with Sonic's DSL is that they are still dependent upon AT&T for the copper lines. I've been fighting with them for 3 weeks to get a stable DSL connection (I have their bonded service). After a tech visit everything starting working better (I think it was a config issue on the router).

But it was quite apparent that for Sonic, AT&T is a big problem. For most of their coverage area, they are still dependent upon AT&T to actually hook their customers up. And AT&T has no interest in maximizing your Sonic ADSL2+. They'd rather you buy VDSL/Uverse from them. I think this is what drove Sonic to start working in Fiber. Not only was it the only way to get gigabit speeds, but it was the best way for them to take control of their own destiny. When you own the fiber, you can make your customers happy. When you rely on AT&T for the copper lines, you are limited in what you can do.

(For the record, I'm in Redwood City and getting ~12Mbps down with 2 bonded lines from Sonic).

That is DSL, where they are limited by the length and quality of the pieces of copper connecting the CO or RT to your modem. Their 100mbit and gigabit services are fiber to the home.

I live in the same area and get decent performance with sonic. Things feel fast. Until recently, I had Verizon FIOS, and Sonic doesn't feel all that much slower (or maybe I've become accustomed to the drop in speed). I love how the DSL just works; I have a DSL bridge, connected to an Airport Extreme, which doesn't need to fragment packets because Sonic gives you the full frame size (another reason I like Sonic). Note that you can find performance boosts just by improving the phone wiring in your home;I played with mine until I found a sweet spot.