I've written a tiny library that implements I2C master functionality on MSP430 devices that only have the USI module (for example, MSP430G2412 or MSP430G2452). It's small, simple, works well for me, and might help others in their projects.
Blog post at http://jan.rychter.com/enblog/msp430-i2c-usi-library-released
Github repo at https://github.com/jwr/msp430_usi_i2c
Have fun!