I think #1 should be the Leighton signing. He signed him BEFORE free agency even began, where there were a few obviously superior goaltenders available. This was clearly a massive mistake at the time, and also clearly indicated the team wouldn't be a real contender the following season...those were just the effects immediately predictable.
In the end, it led to Bob being rushed prematurely into a starting role in a pretty extreme situation, instead of being properly developed. When he started crashing and Laviolette botched the goalie situation, it led to the goalie meltdown that in turn led to Snider's temper tantrum, which led to the disastrous Bryzgalov signing...which led to Bob being traded.
To fit Bryz while filling other holes, thanks to the circumstances created by Homer's previous asset and cap management, the team had to be blown up. Then when Bryz self-destructed, Homer had to take measures to try and shore up his investment in goal, leading to the mismatched personnel. He tried to get Lavi to coach outside of his comfort zone which just led to confusion, it all went to hell, and now we have a team trying to get their game and confidence back. Furthermore, last season was made worse because Michael ****ing Leighton was brought back despite being a terrible NHL goalie, meaning we basically had one failing option in net. So, that brings us to today.
All because Paul Holmgren was unable to make a realistic assessment of Leighton's abilities and signed him early in 2010. What an awful move with awful cascading consequences.
I think this is another example of Homer keeping faulty personnel way too long. Hanrahan is supposed to help him with this stuff, and has failed to point out elementary mistakes. Yet he remains employed.
Overall, Homer has the potential to be a very good GM. He has the creativity and the eye for talent, but his flaws bring him down a lot. He has repeatedly made his own job tougher than it should be and repeatedly put the team in difficult situations, when it's a GM's job to put the team in the best possible situation. He's good at fixing things, but it would be better if he didn't make the obvious mistakes to begin with.
Another bad move is renting Versteeg for a 1st. What the hell was the point of that? I was one of the few who were fine with that move at the time...until he traded him a few months later.