Of the 16 free agents Neal Huntington has signed for $750,000 or more, an astounding 10 were released or dumped in negligible midseason trades
I did some quick and dirty research comparing that record to the other teams in the NL Central, and concluded that his record wasn't all that different from anyone else's. I've since done some more analysis and while I'm not quite as positive about Huntington's record as I was before, the more significant conclusion is that middle-tier free agents like the Pirates have signed in the past five years are bye and large a vast wasteland of mediocrity.
Since Neal Huntingdon took over as GM in 2007, the Pirates have signed 16 free agents to major-league deals. These signings have not exactly set the world on fire - the two most successful are probably Javier Lopez, who put up 0.9 WAR in 50 relief appearances in 2010 before getting flipped in a deadline deal for the totally unimpressive John Bowker and Joe Martinez; and Octavio Dotel, who only put up 0.2 WAR in 41 relief appearances in 2010 but brought James McDonald (and Andrew Lambo) back from the Dodgers. Of the others, only Clint Barmes and Eric Hinske put up positive WAR; the other 12 ranged from Chris Gomez, who managed to be exactly replacement-level as a utility infielder in 2008, to Bobby Crosby, whose .592 OPS combined with subpar fielding to yield -1.2 WAR, to Byung-Hyun Kim, who managed to get released before playing a single regular-season game for the Pirates.
The Pirates, however, have not been in a position to sign top-tier free agents. Their highest-paid FA signings have been Clint Barmes (2 years, $10.5M) and Kevin Correia (2 years, $8M). And it has been rare for free agents in that range (major league deals for one or two years, less than $5.5M/year) to be much more successful.
Since the end of the 2007 season, major league teams have signed 326 free agents in that range. 126 were either released, waived, retired, or (as Dejan put it) "dumped in negligible midseason trades". Another 60 either played out their contracts or are still with the team that signed them, but have put up negative WAR - worse than replacement level. An additional 6 never played for the team that signed them - either being sent to the minors or traded before the season started.
Of the remaining 134, 70 accumulated more than one WAR for the duration of their time with the team that signed them - but only 53 averaged more than one WAR per year for that team, and only 16 averaged more than two WAR per year. In other words, over the course of five years, only about half of MLB teams managed to sign a starting-quality player for the price that the Pirates have been willing and able to pay for free agents (and one of those was Bartolo Colon, whose starting-quality appears to have been chemically-aided).
The bottom line is that free agents in the price range where the Pirates have been playing can fill one of two roles: replacement-level fill-ins to plug holes where the team doesn't have AAA talent ready to move up, or lottery tickets with a maybe one-in-twenty shot. The Pirates haven't hit any lottery tickets - except to the extent that the Two Free Tickets we won with Octavio Dotel turned into James McDonald. And over the past five years, there have certainly been enough holes where the team didn't have the AAA talent to move up.
It's generally accepted wisdom that the Pirates don't have the financial flexibility to build the team through free agent acquisitions. The kinds of players that the Pirates are able to sign in free agency are hole fillers and lottery tickets - and with the improvement of the farm system, they are likely to do nothing more than block internally-developed talent. While there will be more external pressure to ramp up free agent signings as the Pirates see increased revenue as their record improves, the team will be better served by putting that money towards locking up internally-developed talent.