Internal Medicine is a very broad field, and IM residents have many options available to them as far as primary care vs. hospitalists vs. subspecialists. Internists only treat adults (different than family med), and compared with family med, there are a greater number of internal medicine residents who do not plan on going into primary care.
General internal medicine itself is considered primary care, but most of the subspecialties you can do from it are not. Also there are an increasing number of general internists who are becoming hospitalists (physicians who only deal with inpatient medicine).
The subspecialties within IM are quite varied, and they include cardiology, pulmonary, critical care, infectious disease, oncology, hematology, rheumatology, gastroenterology, gerontology, and allergy & immunology. I know there are others I'm forgetting.
I find internal medicine to be a very exciting field which is very intellectual in nature, and offers a huge range of career options, which are some of the reasons I'm going into it. Most IM residents have some idea of what they want to do in IM before they start their residency, although they don't have to know. Personally, I'm planning on doing a subspecialty -- possibly in pulmonary/critical care or cardiology.
Here are some helpful links:
http://nrmp.aamc.org/nrmp/
http://www.ama-assn.org/cgi-bin/freida/freida.cgi
http://www.aamc.org/eras/start.htm