Not using strict or warnings when I first start to throw something together. Then after working on it a few days, spending half a day cleaning it up when I finally remember to put those in.

Spending more time here than coding.

Using terse variable names that I can't remember what they meant after a month, and forgetting to add a comment that would remind me.

I'm also guilty of not enough comments around the difficult to read stuff.

Not having enough fortitude to get the last bits done so I would think that a project is FINISHED. But, part of this is the shifting demands about what is important at the time. Something "important" always crops up toward the end of a cycle, and after working on that for a while it's tough to go back to get the previous project done. It works, but definitely needs some polishing...

-Scott