Take a serious look at the Olympus OM-D E-M5 - if you are doing street shooting, it probably is the best all-round performer with really fast AF. Fuji Xpro 1 (and probably the announced X-E1) has the best high iso and best IQ for sure but the MF still stinks and the AF is not as good. The Sony Nex-7 has the highest resolution (24mp) and people love it but the lens lineup is small. If you already have a m4/3rd set-up I would think the Oly would be a no-brainer.
I keep an eye on these as I love doing street photography and honestly my D300/D800 are just too big, to noticeable, to many MP (D800). I love my X100 but the AF is spotty (much better than what the reviews say-though) but I do prefer 50mm and 85mm-ish over the wide angles.
From mostly research and not much or zero hand holding time here are the basics I have found out of different models for street shooting:
Olympus OM-D E-M5:
Pros: Right now best all around performer - in-body stabilizer superior than anything out there - really fast AF - vast lens choices and accessories. Weather sealed, robust body. Good IQ to 1600, 3200 usable, 6400 nice B&W look to it. Tilt Screen is a huge plus.
Cons: No "real" continuous AF once the shutter is pressed and held the original AF point is locked. m4/3rd "look" - Love it/Like it/Hate it they have a distinct look. Flash system not up to Nikon or Canon.
Pros: Best view finder design - IQ is amazing-Not enough can be said about the image quality- Low light equal to a D700 - Look and feel is really nice. If you like rangefinders you will like the X-pro1. Great glass - Fuji glass has always been top notch. JPEGs better than as Raw on other systems. Slow to fruition but they seem to be building it up quickly. DX format = better bokeh than m4/3. Fuji "look" is really good.
Cons: AF - can't be denied it is slow and hunts in low light. Daylight/daytime shooting (anything above 1/60th at iso 200) it is just as fast as others. MF - stinks. Lenses and adapters are limited but building fast. I haven't heard many enjoying utilizing "other" glass (leica,zeiss, etc.) as there is not a MF focus confirmation.
Pros: Best view finder - IQ is amazing- Low light equal to a D700 - Look and feel is really nice. Fuji "look" is really good. AF has vastly improved with new firmware, probably 3x faster than when it was first released. Leaf shutter-you can high-speed sync flash faster than a DSLR. I can sync my SB900 at 1/1000+. I have been playing with this, and it is amazing.
Cons: Single focal length, MF stinks - AF is OK (just as good or slightly better than compacts). You either like it, or hate it - there really isn't an in-between.
Panasonic DMC-Gx1 & GF5:
Cheapest of the bunch - but still a good system. The Oly has overshadowed this one but it is still a great performer. The GF5 is a really small but good little camera with a 12mp sensor. If you really want to be discrete or want something smaller - it performs better than the equivalent Olys at that size. I have played with these in the store for longer than I should have, and they are really good cameras. Fast AF, good exposure, great IQ (I think a bit better than Oly). For the price, I think it is a hell of a deal - especially if you have existing lenses.
If you want a DSLR in a really small body and 24mp to crop anything, this is it. Many really like adding other glass as it has a great "focus peek" feature. Draw back of it's size is that it doesn't provide in-body image stabilization. It is really pricey and so are the high end lenses. It seems to be a great system. If they had more fast lenses and they were less than $700 than I would be more interested. The MP are more than I want so I really haven't looked at is closer.
Sony Nex-5 - don't know much but it seems to be capable and close to the Nex-7 but with 16mp.
Nikon J1/J2/V1: I have played with these are they are a definite option. Only real drawback I have found is the resolution and if you work in low light, there are better options. It really is a good system for some.
Camera's coming out soon or others to keep an eye on:
Olympus E-PL5, Canon EOS M, Nikon J2, Samsung SMART CAMERA EX2F (Compact that seems really capable and could be an interesting street photog option. Worth a look if you want something really small.), Samsung NX210 is interesting as well. Spoke to someone who is using it and the NX20 and they sound like a really good performing system.
43rumors and Sansmirror are great resource sites along with stevehuffphoto. Steve's site predominantly have street type shooters and always have reviews focused on that type of shooting & is one of my favorites.