When working evenings and weekends, do the fun stuff.
Your tool suite (applications, languages, processes) should vary in a punctuated equilibrium. Make the changes to your tools when you are in a relative lull. Resist the impulse to learn a new tool when your current project is nearing completion, or, worse, when it's nearing a deadline but not nearing completion.
TextMate really does have some fantastic XML indentation syntax highlighter, but will it really help get the project done any faster or better?
An urge to switch tools is often a signal to me that I'm bored or disappointed with my performance.
Try a non-work treat, like that new Flaming Lips cd you've been eyeing, or a few fresh strawberries
If the sun hasn't been out in a while, and it appears, go experience some sunshine. If the sun's out all the time, make some time to sit in the sun.
Sunblock is crucial; don't bring your laptop.
Reading academic research papers and textbooks require sustained, focused attention, which is impossible if you're within ten feet of your computer. Leave the laptop at home and get some work done for once.
Skim giant technical books so that you'll know where to look when you need particular information.
Don't try reading Unix Power Tools cover to cover, but do flip through it, or you might never know what sed can do.
If you're lucky, you work with people who are smarter than you, faster than you, write cleaner code, know more languages, have more experience, etc. Your tendency may be to compare yourself to them, and come off poorly in the comparison. Try this, instead: "Thank god I work with people who are smarter than me, because otherwise I'd be working with people who are stupider than me, and that would suck."
People who are literally geniuses are used to being geniuses. They probably don't think you're an idiot, because they're used to being smarter than everyone else.
Identify particular characteristics of your most effective teammates, and emulate that characteristic.
"Be like Pablo: refactor aggressively." "Be like Scott: keep the codebase tidy, but not obsessively so."
It is almost always a good idea to go for a little walk. (Thanks to Josh Carroll for this gem.)