The users who are really upset are the ones who, wisely or not, used the serve to send important, non-infringing personal and work-related files to themselves, friends and colleagues. Immediately after the shutdown of Megaupload, we saw a surge of angry tweets from people who were using the service for personal purposes and can no longer access their files. Now, there's talk of those users suing the FBI in response.
Several international chapters of the Pirate Party are joining forces to gather the names of users who feel they've been wrongly blocked from accessing personal files. From there, the organization says it will consider filing "complaints against the US authorities in as many countries as possible."
The Pirate Parties' complaint doesn't express solidarity with Megaupload or its founders, but rather it takes issue with the far-reaching nature of the site's shutdown and the negative impact it has had on unsuspecting users who weren't necessarily using the site for anything illegal. In fact, the parties claim that the economic harm done to users by shutting off access to private data could exceed the damage done to the record and film industries by Megaupload's practices.
That's a difficult claim to prove, but then again so is the copyright lobby's assertion that Megaupload cost them $500 million in damages.
Some may find it hard to sympathize with users who were using a service like Megaupload to store files without backing them up elsewhere. While that's certainly not the smartest approach to personal file storage, it also probably wasn't conceivable to many rank-and-file users that the site they were using was suddenly going to get shut down by the FBI and Justice Department. That's not something that happens everyday, even to notably controversial websites.
Many people would use Megaupload similarly to how a service like Dropbox is used: as a convenient way to toss some files into the cloud or give somebody quick access to a project they may be collaborating on.
It's unknown how many of the files hosted on Megaupload were of the personal, non-infringing variety, and it may not be an easy thing for authorities to determine either. It's a safe bet that most of the site's traffic was attributed to piracy-related activities, but that doesn't offer much solace to those who had other purposes in mind.
How serious the Pirate Parties' threats are isn't yet known, but it's evident that they're genuinely displeased with how this whole thing went down, as are many of the site's former users.