Tynan and I had a chance to check each other's cameras out this past weekend. He's pretty passionate about the Sony NEX5 (and some newer versions coming out by Sony). You can read Tynan's blog on the NEX5 here. I'll ask Tynan to provide a few more thoughts on this thread regarding what he likes about it.
One thing Tynan specifically mentioned was the size of the sensor, which is measurably larger than the GX1's (see comparison photos below). As I learn to take great pictures, I've determined that there are a few things that determine how good a photo can possibly be:
1) The skill of the photographer: This, obviously must be learned. A secondary point to this is the preparation that the photographer does to have the right camera with him or her at the right time to be prepared to take the photo. As they say, "the best camera is the one you have with you to take the shot."
2) The specific camera, and it's capabilities: This is where the GX1 vs. NEX5 debate comes into play. And to me, the most important part of the camera is the sensor size. Tynan pointed out that the NEX5's sensor is measurably larger than the GX1's, and he's right. Another factor is the lens used. This is an area where I feel the GX1 beats the NEX5, because it uses the Micro 4/3 standard wehre Sony uses its own proprietary lenses, so you'll likely find much more lens variety with the GX1 over the NEX5 over time.
3) The amount and style of post-processing: Just taking the shot gets you a ticket to the game, but being willing to cull through a lot of bad shots to find the great shot, and then being willing to tease out of the shot the best characteristics of the shot all require patience. And it's also a very arbitrary thing. For example, here's the raw picture of a sunflower I took at a recent Farmer's Market shoot: