I've had the NEX-5 for a few months now.... and I love it! It beats the pants off my a200 in almost every single situation except wildlife photography (the a200 + 70-300G is better). I wanted a better camera and, frankly, Sony was not obliging with any of the recent aXXX series so I jumped to the NEX (I'm still hoping for a decent updated a700 though I fear I'll be disappointed). I carry the NEX most of the time now (family outings, walks etc) because it's convenient and gives me the quality I'm after. I only bring the a200 when I want to use one of my A-mount lenses for a particular subject.
The photo quality is amazing, particularly the high ISO. I'd never go above ISO800 with the a200, and even that would be grudgingly and I'd probably throw the shot away (normally I'm restricted to ISO100-400). The NEX is very good up to ISO1600, and Lightroom 3 does a very good job of removing that noise. I never thought ISO speed was a big deal (particularly the insane high ISO modes) but having great quality images at ISO1600 opens up lots of possibilities. The liveview also makes night shots (i.e., star trails or even IR photography) much easier because you can see the exposure and use the LCD to focus manually.
Feature-wise, the sweep panorama, auto-HDR and handheld twilight modes are very good and useful too (though not infallible). The menu system is a little odd but it doesn't take long to get used to. The forthcoming firmware update will fix most of the issues though I'd live with the current system. I'm looking forward to the new E-mount lenses and seeing what some fast/sharp glass will do for the images.
If you're interested, I wrote a full review for Warehouse Express, including sample images: http://blog.warehouseexpress.com/sony-alpha-nex-5/
There's a few more full-res *unprocessed* images here: http://hopeless.smugmug.com/Photography/NEX-Samples/13413653_r9W9X#976048874_Cn2sb
Hope that helps.