I have a Saleae. It's pretty useful. I was going to mention that Dave's previous blog pretty much covers these in general, though he only passingly mentions this type that doesn't use a buffer, but real time streams over USB. It's good for hobby work and I do a lot of interfaces with SPI, I2C, serial, and parallel data streams. The only limitation I've had is that 8 channels was not enough for a 8bit parallel data interface with 4bit address that I've had to do.