I've used it quite a bit, and it has it's advantages. One of them being that energia sketches can be imported into code composer studio (free from TI) so that you can debug your programs properly (could be that the Arduino/AVR has the similar toolchain, didn't look for it, but it worked very well with MSP).
Also, the MSP's are extremely 'project friendly' in that they run off 2 x AA batteries, down to 2.1V or thereabouts (*), are very low power and runs without a crystal.
Could be that Arduino offer similar advantages, I'm sure the experts will be able to chime in.
(*) Such low supply voltages on the MSP430 requires a lower clock frequency than what the standard Energia setup uses, but it's very simple to add a piece of code inline in your sketch that reduce the frequency to e.g. 8MHz, so that you are witing 'SOA'.