I have two of these, the Nexus 7, the Kindle Fire and a half dozen others. (App developer here).
The first thing I did with the Samsungs is to ROOT them and remove all the crap-ware, especially KIES. Samsung as pre-installed a number of apps which may or may not serve a purpose, but in the end have full access to anything on your tab AND internet access as well, so if their systems are compromised, they can have at your personal data.
That said, I prefer the Nexus 7 for everyday use. Battery life of the Nexus 7 is significantly better than the Samsung devices, with a good week on standby and light use for the Nexus 7, vs. three days tops for the Samsung. What's worse, Samsung has a proprietary charging cable, so there's additional expense there if you want to remain flexible.
Samsung's GPS receiver is better, and of course, it's got a rear camera and the MicroSD slot. On occasion, I would have liked a rear camera on my Nexus 7, for apps like Google Goggles or Google Translate -- however, the Samsung camera's resolution is nowhere near enough to do proper OCR anyway.
My Samsung tablets are used as media players for the kids, so the SDHC slots are permanently populated with 32GB cards -- something that the Nexus doesn't have. Samsungs easily last through three movies, 6-8h of reading, and 4-5h of Cut The Rope.
The screens are equivalent, with a slight edge to the Samsung. Performance of the Nexus is, as expected, better.
If you want a cutting edge 7" tablet with all the bells and whistles, for everyday use (calendar, email, browsing), get the Nexus 7. If you are planning on consuming a lot of media on the go, and you need the microSD slot, this is a decent deal, although I'd like to see it closer to $150.