Hype typically translates to inflated draft position, which negates any potential positive investment value. Also, people typically identify young players with HR/SB upside as popular sleep targets. Most of these players also have terrible plate discipline.
Difference is that hype on Encarnacion is a lot more muted this year, from what I've seen. Even though the guy managed to hit 26 HR in 506 AB this past season -- actually a good power demonstration -- he's been going anywhere between the 16th and 20th round. That's pretty good value for what he had just done, and doesn't account for the upside of growth.
Secondly, I disagree with the first poster on this thread. He actually doesn't strikeout too much. He actually is fairly average when it comes to strikeouts. But what separates him from most young players is his ability to take a walk. Last year, he took 61 free trips to 1b, a pretty decent number. He's actually shown a bit of plate discipline growth that would warrant attention.
In short, not sure why people are so down on his production in 2008. He made good strides yet his draft position has fallen. He has upside still as he's still relatively young. That's what makes him a sleeper in my mind. As of right now, of course. Maybe people will wake up.