I lived and trained in Charlotte for 7 years before relocating to Virginia where I live now. I would say CLT is a decent but not spectacular place to train. For one thing, it is close to board-flat (no place is totally without SOME hills but for the most part, it is flat) which limits your training somewhat unless you plan to race locally or on flat courses. There are plenty of well-maintained tracks you can use. The number of races has grown substantially over the years and if you are willing to drive you can find races just about any weekend. I think there are some knowledgable coaches/running authorities in the area and would suggest Larry Frederick at
www.runforyourlife.com
(he'll email you back) and Scott Dvorak at Charlotte Running Company. Scott was in the OLY trials for 5000 a few years ago.
Cross training wise you will find cycling difficult unless you are willing to travel well outside city limits. The city has grown quite rapidly and a few ago was listed in USA Today as one of the 3 fastest growing cities in the US. Simply put, the demand outstrips the supply. Over time that may improve if the city planners will think progressively. Clean air is a problem!! Folks have mentioned the humidity but in the summer the smog is quite heavy. CLT carries a poor air quality rating.
Socially and in terms of quality of life a lot will depend on who you are and what you are looking for. It is a good place for a family and fairly affordable but public schools are a problem and private ones cost 5-15K a year. As a single person the dating scence is not bad as the two major banks tend to attract young professionals. there are plenty of blond cuties in Beemers tooling around. Dating thru the running scene gets a little incestuous though.
all in all CLT as a place to live is not missing on much. it certainly is night and day different from Denver tho, both in terms of the type of people living there as well as climate and terrain. If I were placing running as a one of my top 2 or 3 priorites in life it would be a no-brainer for DV over CLT for me.
Best of luck wherever your travels take you.