Question: I have never really understood the connotation of someone calling their domicile a *condo* over the word *apartment*. I have a vague feeling the former is fancier and more up-scale, but are there any real differences I'm not aware of?

Answer: 
In the US, a [condominium](http://www.merriam-webster.com/dictionary/condominium) involves an investment of funds, and is similar to buying a house. A person actually owns a condominium and can sell it for a return on investment. Also, they can use it as collateral for borrowing money.

An [apartment](http://www.merriam-webster.com/dictionary/apartment) is rented/leased from a landlord/landlady. Rental payments go to the owner, and the tenant does not own the property, so cannot borrow against it. When a person moves out of an apartment, they may receive their security deposit back, but that's about it.

I think owning a condo probably is considered more high-class than renting an apartment. Many, many rich people in New York City own condos, for instance, and brag about it.
Something none of the answers have pointed out yet is that the meaning of *apartment* is **different** in New York City and in most of the rest of the U.S. In New York City, an *apartment* is a single unit in a multi-unit residential building, regardless of whether you rent or own it, and of whether the ownership is legally a condo or co-op arrangement (so *apartment* in NYC means the same thing that *flat* means in the U.K.). In most of the rest of the U.S., an *apartment* is a *rented* single unit in a multi-unit residential building. 

This means that in most of the U.S., if you live in a multi-unit residential building, you either live in an apartment, a co-op, or a condo. In New York City, and in much of Canada, your *apartment* will either be a rental, a co-op, or a condo (or a sublet, if you lease it from somebody who in turn is renting it themself).