Just to clarify up front, what you're most likely to get are a series of endorsements for the particular camera each person has, or advice to just move to a compact DSLR instead (from people who have those compact DSLRs). Truth of it is: They're all good, so pick based on features, price, what you like, and what feels good in your hands.
That said...a few things I'd add for consideration:
1. The Sony NEX systems (NEX3 and NEX5) both come with a flash in the box - it's a small external attachable flash. Many folks just stick it on and leave it there, since it's so tiny it's only 1/2 inch tall on top of the camera in the 'down' position.
2. The Oly Pen and Panasonic G systems have built-in stabilization in the camera body, whereas the NEX would require purchase of lenses with stabilization in the lens.
3. The NEX system has a larger APS-C sensor, as opposed to the Pen and G micro 4:3 sensors - the NEX sensor has better low light performance at higher ISO levels.
4. Currently, the Pen/G system has more lenses available to it - though both lines don't have nearly as many as with DSLRs. But both the NEX system and Pen/G systems have more lenses coming soon, and both have upcoming 3rd party lens support.
5. Both NEX and Pen/G can accept various adapters which allow them both to use almost any camera mount on earth on these camera bodies, but would require manual focus and aperture control when using those lenses.
6. The Pen/G cameras have a slightly more adjustable settings in a more traditional layout; the NEX cameras have a new menu architecture that has been overhauled with a firmware update that improves the customization from the original highly criticized layout.
7. The NEX cameras have a tiltable hi-res LCD, allowing variable shooting angles. The Pen cameras have an electronic viewfinder accessory that can be purchased.
That covers a few of the things to know. Both camera systems will be capable of shooting in full auto mode, pont-and-shoot style, far better than any P&S camera can achieve in challenging lighting situations. Both systems will allow growth in photography, with more advanced controls, priority modes and full manual modes, and ability to change most any parameter as you learn what and how.
I recently decided to pick up one of these systems as a 3rd camera - in between my little ultracompact P&S and my DSLR kit. I chose the Sony NEX3 for myself, based on the factors that were important to me personally and my style of shooting: price was good, build was good, it was comfy, very small, with the firmware update the controls are now intuitive and customizable so all necessary manual functions can be changed with direct access buttons on the body, I liked the tilt screen, and I really liked the high ISO performance. I would have no qualms recommending the Pen or G series cameras if someone found they liked the feel, the images, the lenses, the menus, or just the brand itself. I don't think you'll find a bad one between the three systems.
I know I likely wouldn't be happy with one of these cameras as my only camera, but that's because I do lots of heavy photography shooting - wildlife, sports, low light, architecture, etc - and these cameras are designed more for travel, scenic, all-round, and hobby shooting. I have set up the menus of the NEX3, and tuned all the default settings and modes to my style, and have thoroughly enjoyed it so far, especially the low light capabilities which are astoundingly clear and detailed even at ISO6400...very usable for just about any setting I'll be in. And I love the look of the camera too. It works for me, but maybe not someone else, so by all means, handle the cameras and see which you tend to favor, then compare features and prices to hone down which is best for you! If you end up interested in the NEX system and have any other questions about it, I'd be glad to answer what I can.
