Regarding comparisons between the ooma and obi, here are a few of my thoughts:
I have both ooma and obi and use ooma for our main home line. I have also recommended it to my friends and family. Both my parents and my in-laws have switched to ooma with (mostly) good results.
I bought the obi after the ooma was in service as our home service and haven't had enough incentive to switch. Here are some reasons:
1. I remember reading that ooma runs everything over a vpn between your unit and their server. Google might also do some encryption (I don't know), but it would be hard to beat that security provided by the vpn.
2. Obi works because their developers were able to trick google voice's servers into thinking they were communicating to a google web client. Google could change their protocol with no warning and break obi. Whether obi can correct this with a firmware update in a matter of hours or months, I have no way of knowing.
3. If you desire to keep a previous number, consider that Google only ports mobile phone numbers. If you wanted to preserve a home number, you would need to port twice, first to a mobile phone, then to the Google Voice number. Ooma will port both fixed and mobile phone numbers
4. Yes, it is possible that ooma could go out of business and just pull the plug. That's a calculated risk, but one that took just a few months to pay off.
5. Ooma's 911 service at least connects to an emergency operator, sending along with the address you enter during set up. While not perfect, I know that if a visitor to our house or babysitter picks up the phone and dials 911, help will come. There are some work-arounds with the Obi, but they seemed more brittle than the ooma solution.
6. I bought the obi more as geek project. Perhaps with more time, obi will develop the reputation as "ready for prime time", i.e. ready to go in the homes of your non-techy friends and family. At the time I got my obi, the majority of those who recommended the obi were fellow geeks. Ooma has been around a little longer.
Despite all of the above, had ooma not been available, I would likely have pushed harder to deal with the above reservations. None seem insurmountable. Maybe it is time to give obi a deeper look. But I am happy with my ooma, and suspect most woot customers would be as well.