Whilst I generally agree with Mr Rath, their are a couple of things I feel aren't quite clear in his article, a couple of additions I feel should be in their, and the odd disagreement.
First off, I would say that the fedora is an informal hat, rather than a dress hat - however "informal" (the context of menswear) generally speaking means a business suit. Formal is a white tie [http://www.blacktieguide.com/White_Tie/Tailcoat/BB_golden_fleece_$1600_2009.jpg] (evening) or a morning coat [http://andrewsandpygott.files.wordpress.com/2011/01/sdc13469.jpg] (day). Semi formal is black tie [http://cdn.shopify.com/s/files/1/0033/9922/products/P2360424_grande.jpg?v=1393852906] in the evening and a black lounge suit/stroller/Streseman [http://i595.photobucket.com/albums/tt39/andrewspygott/SDC16997.jpg] (it has many names, and is nowadays pretty much defunct) during the day. You can also just about get away with a fedora with clothing from the most formal end of the casual scale - tweed jacket and flannels, no tie, with leather "dress" shoes is perhaps the most casual you can get away with and wear a fedora.
Okay, now the reason for that odd sidetrack about menswear formality terminology. A black hat is worn with formal and semi-formal wear; a fedora, as discussed, is informal. A black fedora is therefore a bit hard to wear with anything, as well as being atraditional (outside of a couple of very specific contexts - Vicars and hasidic Jews, primarily) being too casual for semi formal and too dressy for informal; homburgs (and, during the day, bowlers) being "correct" for semi-formalwear and top hats for formalwear. With that in mind, avoid black fedoras - they just don't work; it's a bit like a tweed dinner jacket.
I'd also add that the hat colour should really go with the suit - a brown hat with a grey suit doesn't look very good. Grey with grey, grey or blue with blue, brown or fawn with brown, brown or biscuit with khaki, etc.
However, proportions should also match. A jacket with skinny lapels looks strange with baggy trousers and a fat tie, similarly a jacket with wide lapels looks strange with a narrow brimmed trilby. Keep tie, shirt collar points, lapels, and trousers width proportional with the hat brim. If they are all narrow, you need a narrow brimmed trilby (like Frank here [http://i.telegraph.co.uk/multimedia/archive/02526/sinatra_2526239k.jpg]). If they are all wide, you want a wide brimmed fedora, like George Raft [http://2.bp.blogspot.com/-Z2Rs5nO5Pyw/Tig1O2cUncI/AAAAAAAAAEg/2JCcOc2YCsw/s1600/1930%252527s%252BGangster%252B-%252BRaft.jpg]. Nowadays, the fashion is for skinny everything, so best bet is a narrow brimmed trilby.
Oh, and if you also need the haircut for it. Short back and sides, shaved, crewcut, all work. If your hair requires a hairband, or extends beyond your collar, or is described as "business at the front, party at the back" avoid the hat.
And yes, I do usually wear a fedora (wide brimmed). I also usually wear a suit (I need to for work); my suits and ties are all from the 30s or 40s.
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