There are no GMs that make zero mistakes, so if those are his worst transgressions we're in good shape. Svech, at best, would have been a third line winger, Regula looks like a depth defender (I thought he'd be better), and Cossa still projects as a starting goalie (even if he doesn't end up better than Wallstedt). He's made no glaring mistakes and has some considerable "wins" to his credit (e.g. mid to late round drafting, the Debrincat trade, the Walman trade).
I guess you could say the Chiarot and Holl contracts are "mistakes" but neither of those deals block any young guys from playing time and it's not my money, so I don't think they're all that bad. If guys like Wallinder and Edvinsson can't (eventually) beat out Chiarot or Holl for a spot on the team then they're not ready to play in the NHL anyway.