I have been looking at ads from a couple of companies in Shotgun News offering mid-length barrel uppers, these are the 16" barrels with the handguard about halfway in length between the shorty and standard rifle length. That is about as much as I know, other than I think they are a much better looking configuration, than a standard shorty. Can anybody fill me in on them, or point me to a good thread? TIA

Do a search.

Here's one of mine on my Armalite mid length 16":  

http://www.ar15.com/forums/topic.html?b=3&f=118&t=204310

I think RRA and Armalite are the only ones who offer them.

I have been told that they have slightly less pressures in the chamber and that they may last longer due to less stress. I may be wrong but I like them. Here are my two RRA mid-lengths.

M&A Parts has mid-length kits.  Here's mine on an Eagle arms lower:
...oh yeah, with some coy. brown Cav. Arms replacement furniture....
http://apastron.150m.com/pics/ar_02.jpg