I decided to go ahead and include them even though they're not 100% confirmed to be scams (and chances are, we'll probably never know), since many of those in the community think that they were scams. Not to mention there seems to be a general consensus that even if they weren't outright scams, their owners were still negligent with their users' funds or dishonest at the very least.
That being said, I should also point out that there have been occasions where scammers actually admitted to their scamming behavior. Stackcoin is the most memorable example:
never forget!
ah the good old days

We didn't forget ahah

Still waiting for this gif to be the official alt-coin logo !
Thanks to everyone for the 69.5 btc, don't worry they have been well spent ! And thanks to the guy who sent 0.5 more to make a round 70, also for the retard who sent some btc 3 months after !
STACKCOIN WILL NEVER DIE ! NEVER FORGET YOUR LESSON !
WE WILL COME BACK
BETTER
STRONGER
STAY TUNED FOR THE BEST SCAM EVER !
The most recent example was the "Evolution" Darknet which happened earlier this week:
Bitcoin Scammers Run Off With $12 Million: Going to The Caribbean
Hope You Guys Understand
The most recent example comes to us from the Evolution Darknet, which according to a report from Crytpo Coins News shut down their web server and ran off with $12 million in user bitcoins...
Ill be around around for a short period of time before permanently moving to the caribbeans, I hope you guys understand.
Source:
http://www.zerohedge.com/news/2015-03-19/bitcoin-scammers-run-12-million-%E2%80%9Cgoing-caribbean%E2%80%A6-hope-you-guys-understand%E2%80%9DWow, I didn't know about these. They are disgraceful, I don't know if you believe in such things but I do believe in Karma and people like these always get their comeuppance. Good luck with your venture, you'll never have shortage of content. If you do, just take a gander at "Investor-based games", it's a new playground for scammers.