1. Not being loyal to my bigger goals.
I started with IM and it actually worked nicely, wanted to scale up but then being a freelance programmer as well, got some big projects for good cash. Went ahead and did them (so far so good), but then got carried away with this type of 'immediate money per hour' mentality and neglected my bigger goals for a long time. It eats up your soul and then you end up starting from scratch (unless you want to be a per hour programmer for the rest of your life).
2. Spending too much time on little things/perfectionism (typical for programmers btw).
Back in the link spamming days. So got to know Sick Submitter inside and out. Got to know ZennoPoster inside and out. Got to know SeNuke inside and out. And so on. Takes too long, too much effort and time for too little gain.
3. Coming up with too intricate plans to achieve too little. Concentrate on the big stuff - building stuff that converts to money.
There's a lot more but these 3 poped to mind.