I've used both quite a bit at this point, the GF1 more than NEX given how long they've been on the market. They both work pretty well for street shooting.
I decided to keep the NEX because the color and the flexibility of the files is more to my liking, it does somewhat better with wider M lenses, and it is smaller, but the truth is I actually prefer the handling of the GF1 and you have the option for EVF if you need it. Also, better native lenses for GF1 at this point -- if you are an autofocus person, the GF1+20mm with center-point AF set is extremely handy and fast. On the other hand, new E lenses are apparently on the way.
If you have a chance you might want to try both out in person -- one may just feel better to you. Note also that both manufacturers are innovating in this area so there is always the possibility that one system or both could deliver significant advances over the next year.