I've been using the Nexus 7 for a couple of days now and am really happy with it.
The only limitations compared to the Tab 2 are the rear facing camera and the built in SD card slot. I really don't see a tablet with a rear camera as a replacement for a proper camera... the only advantage would be if needing to add images to an eBay sale or forum post, where it could be handy. The card slot is an annoying omission from the Nexus 7 but I read it was to avoid paying Microsoft licensing fees, and you can connect external storage to the USB port anyway so all is not lost.
Otherwise the N7's screen is instantly nicer than the Tab 2's and the hardware is noticeably more responsive. Also some games are being released in optimised versions to take advantage of the 12 core nVidia chip.
I've also decided a 3G enabled tablet is a pointless expense, especially as you then need a mobile data sim and monthly contract with more expense. I've been tethering my Nexus 7 to my Sony Xperia Play when out and it works perfectly. I've used the internet, downloaded apps, used Google Maps for driving navigation and more. All worked perfectly.
The Samsung Galaxy Tab 2 also has one limitation I hadn't realised before we bought one. It has a proprietary connector instead of a USB port. This means to charge it you need to have its connector to USB cable that came with it, whereas with the nexus 7 it has a standard microUSB connector so I can charge it from my phone charger, from the microUSB charger in the car, connect it directly to a computer to charge. So that is a bit annoying and IMO another advantage to the N7.