Has anyone ever booked a business class fare using any of the numerous websites that advertise "discounted" business class? I got a quote from one of these sites and the price was certainly attractive. Maybe too attractive?

Cindi...No, but it appears that many carriers offer "published" discount business class fares.They are capacity controlled, and most require fairly hefty advance purchase.IE, I got a BC fare to London (from LAX) $2,950.00.I have also gotten reduced business class thru AmericanAirlines Vacations for under $3K DFW to Paris.The AA Vacations package included hotel/hotel tax/and transfers.But I have not used any discount sites.Hope this helps and best of luck!

Sometimes the "discounted" business class tickets through these websites are award tickets.

Have you checked the airlines directly? As BeachBoi said, most carriers offer published discount business class fares.

What sites have you checked? Ebay always has people auctioning off plain white envelopes that have upgrade certificates thrown in for "free."

Carrybean-
The site that I got the quote from was planetamex.com. I was looking for business class to the Maldives on Emirates. They quoted me a fare roughly 50% off the Emirates business class fare listed on the Emirates website. I questioned whether this was a "bulk" ticket and they replyed that it was not.

I fully understand you getting such a deal with Emirates, in the Gulf/Asia region airlines discount First and Business just as much as they discount coach/economy. If I heard of someone paying 'full published fare' I'd be dazed!
I recently had to get a relation a Business Class booking Singapore to Shanghai, about 7.5 hours flight, was just under USD 800 return, a Business Class fare from South East asia to Europe would range depending on season and airlines probably between USD 1.5 to 2k.
It's normal to go through brokers/agents who advertise in the local press, another ticket we bought ( Coach ) for an 8 hour flight duration was about USD 320 return on a good airline ( Gulf Air ).
I think a lot depends on the route you are taking and what airlines operate, the Cindik example with Emirates is an example, they are now uping to 3 flights a day from JFK to the Gulf and onwards and they have 'always' heavily discounted 'all classes'.