The most time I've ever wasted...
...other than being on El Reg instead of working, was when I was given a Racal (iMilgo?, -Vadic? eh, lost to the mists of time) modem that ran 28,800 at a time when I was connecting my Mac through a terribly expensive 1200 modem. I spent soooooo many long weeks trying to get that modem to work to connect to all/any the BBSs at the time. I tried connections through both legit and dodgy purveyors, determined to suss out the key to getting that thing to work. No nice universal search back then, alas. It all came to a crushing end when I eventually found out that the modem was a synchronous beast designed for point-to-point comm with a similar modem for corporate use and incompatible with the common kit used in less-rarefied spaces.