No Its literally the same exact car. The only difference, as already stated above is that the G37 sedan has a larger displacement engine. The 2007-2008 G35 sedan composed a 3.5 liter V6 producing 306 HP hence its name the "G35" while the 2009 model received a revised 3.7 liter V6 engine producing 328 HP which quickly prompted its name to a G37 sedan equivalent to the G37 coupe. Minor revisions where given to the 2009 G sedan model but nothing aesthetically different or even noticeable that would differentiate the 09 model from the 08 model. Other then the engine, the 2009 model received new knobs for the heated seat settings, white background illumination for the LCD infotainment system & for the Drivers Gauge display. It also received a new seven-speed automatic transmission to go with it compared to last year's six-speed. When you really start seeing a noticeable difference between the G35 and G37 sedans is when you compare the 2010 models which where face lifted and revised both in and out.
Here are the minor differences between the G35 & G37 sedan:
(Identical exterior)
2008 G35:
http://www.roadfly.com/new-cars/wp-content/uploads/gallery/2007-infiniti-g37-sedan/infiniti-g35.jpg
2009 G37:
http://strumors.automobilemag.com/files/2008/10/10923785.jpeg
(Heated seat knobs)
2008 G35:
http://media.caranddriver.com/images/media/35762/2007-infiniti-g35-heated-seat-controls-photo-39466-s-1280x782.jpg
2009 G37:
http://0.tqn.com/d/cars/1/0/Z/d/1/ag_09g37_heatseat.jpg
(Dashboard gauge display)
2008 G35:
http://buyersguide.roadandtrack.com/media/eVox/stills_0640/4832/4832_st0640_062.jpg
2009 G37:
http://image.automotive.com/f/2010_infiniti_g37/2307267156665041673+w500/gauges.jpg