Hi, I'm Mauro Soligo from Italy, I'm searching a programmer ( payed ) to develop a code ( can be relased as OpenSource ) to use an Arduino Micro as SMBus PC interface ( similar to I2C ) .
My idea is to use this "system" to connect at a linux pc some SMBus device, In Kernel source there are driver but on some PC ( Small Embedded PC ) there isn't SMB port...
I'm only thinking that your project is harder than implement I2C PC interface because the Arduino have not a SMBus implemented by hardware.
But I think is a good idea for a project anyway.
I2C is no very different from SMBUS 
I need to comunicate with LTC4100 IC ( LTC4100 Datasheet and Product Info | Analog Devices ), I'm working on a BatteryCharger for robots http://robodiscovery.com/robopower/
USB-I2C adapter was build with an FTDI IC but it's only slave I2C IC, I will change this part of project in future if I find a solution with Arduino.