Yes, I have done what your asking about. I have the Astro Devices Nexus on my 16" GSO dob, and run Sky Safari Plus for full Pushto functionality. I can say that it is a fantastic open system, and low cost compared to old style proprietary systems like Argo Navis. I run a Nexus 7 tablet (don't be confused by the same name of the two devices, the Nexus 7 tablet is a Google Android tablet). If you want Pushto you will need to use Sky Safari Plus, not the free Sky Safari version, but it only cost $13 for Google Store.
You can in theory run Sky Safari Plus on an Android phone that has wifi, but really a larger screen is much nicer and a 7" tablet is probably a good size. You can easily mount the tablet on a stalk attached to your base (using one of the many windscreen suction attachments).
Re Bluetooth and Wifi, the Nexus box is the wifi solution and the Betti box is the Bluetooth solution. I use the Nexus Wifi, and it is rock solid and will hold a scope connection up (without drop outs) for the entire night.
I am using US Digital 10,000 step encoders. Talk to Serge at Astro Devices, he can supply the cables you need to connect to the encoders, and maybe the encoders if you ask him.
Now you wil need to setup your dob to mount the encoders and really that's the hardest part. There are places on the Net in the US where you can buy new pivot bolts which can be used for both the Azimuth and Alt pivots. For GSO/Bintel dobs, the Alt bearing will require alittle modification in order to get the encoder bolt into the centre of the bearing so that it rotates with the scope movement. I am happy to share how to do that. Be aware that Argo Navis do provide a bearing modification service (which you pay for) but Gary will only sell it to people buying a complete Argo Navis system from them ( I know this because I tried). Don't be put off by having to mod the bearing as it's pretty straight forward. I am happy to talk you through it when your ready, there is a low tech way to do it that won't cost more than a few dollars, you certainly don't need a machine shop or fancy tools (well a drill would be needed).
You can purchase the pivot bolts (need two) for the encoders from these guys:
http://www.astrosystems.biz/pivot.htm
A Nexus/Sky Safari system while Pushto in the form described, is capable of driving Goto with the install of Servocat Jr motors. Serge can explain it all. The abiliity to use the Android open system, low cost applications, and the database features of the system that allow visualisation of objects, movement, etc leaves the old hand controller based systems in the dirt.
BTW I have a Goto mount on my small newt and the Nexus/Sky Safari system leaves it for dead in terms of use and the ability to visualise what is going on, and it is much faster than a motor driven goto system as you can move the scope by hand just using the target display. It's wonderful to watch your scope track across the star field as you move from target to target. ALignment is easy.
