As long as someone isn't looking over your shoulder and your computer is free from keylogging software, what you type should be pretty safe...or it was, until researchers learned to read your keyboard's electromagnetic radiation.
While two separate teams have developed a variety of ways to sniff out your typing from a nearby area, my favourite involves just $5,000 worth of equipment: a PC, antenna, oscilloscope, and an analogue to digital converter (use your government coupon!).
With this rig, they could decode what most keyboards were typing (with 95% accuracy) from 22 yards away. Laptops proved the hardest to read because a laptop keyboard's electromagnetic signature tends to mix with the rest of the system. But those fancy, wireless encrypted keyboards? Easy. Apparently such a keyboard identifies itself with every keypress because it passes an encryption algorithm. Once identified, it's decoded like any other keyboard.