Although entirely possible that celblazer knows something I don't, I believe the flow meter actually connects to the arduino, not the kegberry. I had hooked mine up initially to the kegberry instead of the tablet and had basic functionality working but not everything. Here is how it's hooked up:
Flow meter -> Kegboard (Arduino) via input pins
Kegboard -> Tablet via USB
Tablet App -> Kegbot-Server via WiFi (optoinal)
A few definitions might help:
1) Kegberry - this is a Raspberry Pi mini-computer that runs Kegbot-Server. As mentioned in the thread, this is optional and you can run with just a tablet. I think using a server/kegberry adds extra features, but I'm not sure exactly what is and isn't included in a tablet-only build. I had a rPi anyways and wanted to build with that so I never investigated tablet only.
2) Kegboard - this is your Arduino. There are plans on the site for building your own kegboard with relays, etc. but this is NOT necessary. Just buy a basic Arduino, plug it into the USB drive of your computer, download the Arduino IDE and write the firmware to it, which only takes a couple minutes.
3) Flow sensor - This goes in-line in the beer line and plus red-5v black-ground yellow-port 2 on your Arduino. The cheapies work just fine. I'm using one from ebay that was only a couple bucks. A second sensor would go into port 3.
I have mine running on an Arduino Uno right now, so I know that works. You can buy 'generic' arduino boards in many different flavors that I assume would also work fine. I have ordered a generic Leonardo, a Mega, and a Nano and plan to test each of them but they haven't come yet. I can vouch 100% that this works (although more expensive than the generics.) I can report back once I get my generics that just cost a few dollars, but they are coming from China so who knows how long they'll take.