Just notes on a couple players mentioned already...
Christian Dube's problem wasn't that he wasn't good enough. He certainly was/is good enough. The problem with him is the NHL was never his goal. He grew up in Switzerland - I think he was there for eight years - and his ambition always was to return to Switzerland. He loved it there, and players in Switzerland make a great living for half the schedule and a fraction of the travel. The moment he got the chance to go to Switzerland, he bolted. I don't know if his love of Switzerland factored into his draft position, because I think he had the talent to be a second line playmaking centre in the NHL.
Evan McGrath had a ton of hype after winning the Memorial Cup with Kitchener in 2003. It wasn't just a matter of the hype occurring after he put up big points in 2005. He was a consensus top 10 pick entering the 2003-04 season. Then he had about as bad of a draft year as one could possibly have.
The player who came to mind for me right away the moment I saw the title of this thread (since he was a player who was heavily hyped on these boards since I've been a member) was Anton Babchuk. I know he was a first rounder, but when it came time for HF's semi-annual prospect rankings, he would finish in the 20-40 range. I was never impressed with him. He had the booming shot, but I was left wanting more in the other elements of his game. I know it's early in his career, and he still has time before he's classified by some as a disappointment, but I think my hunch on him will prove correct: a big, hard-shooting, third pairing defenceman.
On Dube, he was very talented and looked like he belonged on the Rangers in 97, but that was the year that NY got burned by the Lindros lead Legion of Doom and the big bad Flyers, so the small Dube who in the regular season was constantly knocked off the puck by larger players was told to get bigger and add weight by the size obsessed Neil Smith. Dube came back in the next training camp 20 (25?) pounds heavier, and couldn't skate at an NHL level. Soon after toiling in the minors he bolted for Switzerland. He was mishandled, the Rangers expected him to be something that he wasn't and didn't wait for his game (based on speed and skill) to develop after one year.
A similar thing happened after the 95 loss to the Flyers, Neil Smith traded Sergei Zubov, and Petr Nedved to the Pens for size in Robattaille and Ulf Samuelsson after Lindros and Philly physically dominated those two. Some people may not remember, but Eric was a behemoth in those days who literally scared little kids.
On the Detroit prospects, after striking gold with Datsyuk, and Zetterberg, along with the Shanahan quote/joke about the Wings' European scout being the best in the business, Griggs, Kronwall, Hudler all got some extra unwarranted hype. At the 02 draft, people said Hudler was a top 10 talent but too small, but once Detroit picked him, he was called an automatic 40 goal scorer.
Btw, from what I remember from the earlier days of these boards, Doc Chimeara had an unhealthy attraction for Russian players, some of the posters here kept asking him if he was Mike Smith.