Pentax has a new entry into the growing compact interchangeable-lens camera category.
Two other digital cameras also in this category are the Sony NEX-7 and the Samsung NX200. There are, of course, several others. I mention the NEX-7 and the NX200 because they're #1 and #2 (respectively) in the compact interchangeable-lens class and a good point of reference.
The sensor and software found within the K-01 are not new, but are from the K-5. In fact, the K-01 is basically a K-5 but without a mirror and in a much smaller body. Considering that the MSRP of a K-5 (with a lens) is $1,750, while the MSRP of the K-01 (with a lens) is $900, the K-01 is a great value.
The technology found within the K-01 is almost two years old, which, in the digital world, is old. Pentax simply put that technology in a smaller, lighter, cheaper and better looking case. I don't see the K-01 attracting new customers to Pentax, but it should be a very good option for those who already own a Pentax DSLR.
The K-01 has an APS-C sized sensor with 16 megapixels, which is more than enough to craft great photographs. The camera has plenty of resolution for 99.5% of photographers. Some professional photographers use the K-5 as their primary camera, and the K-01 is equally as capable as the K-5.
Pentax also has pretty good built-in software that allows you to do many post-processing functions in-camera, which is great if you don't own Photoshop (or you don't have access to Photoshop because you are on location, but need a finished product ASAP).
The biggest advantage of the K-01 is that it can accept any K-mount lens. Your lens choices are almost limitless! While other cameras in this class typically have less than ten lens choices, K-01 owners have hundreds of lenses to choose from. Second-hand lenses can be had for very little, and if you already have a Pentax DSLR, you probably already own all the lenses you need.
The Pentax K-01 is not as good as the Sony NEX-7 or the Samsung NX200, but it's not far behind, either. If money is not an issue and the choice is between the NEX-7 and the K-01, then go with Sony, no doubt about it. If the choice is between the NX200 and the K-01, then it is a more difficult decision. If you want the most lenses to choose from or if you already own a Pentax system, go with the K-01. Otherwise, go with the NX200.