I'd definitely recommend MFNR, or Multi-Frame Noise Reduction. ; It's the same technology as the 'HHT' or Hand Held Twilight function already on the NEX, but it steps it up a notch by allowing you to use it in any of the PASM modes, with full user control over any or all camera parameters and settings. ; HHT stacks 6 frames, but as a scene mode, with no ability to set ISO, focus point, metering area, etc. ; With MFNR, you can do 6-frame stacking with all the control you want (My DSLR has the MFNR feature, while my NEX has the HHT - I use them both, but LOVE MFNR more!).
The time lapse functionality looks cool too - with the ability to use it in video and stills modes.