Amen Michael! A single test pin has saved my backside many a time. Combined with ISP so you can quickly move the code that wiggles the test pin and it's pretty useful. Combined with a scope it's great, but you can get by with a logic probe.

At one point I went as far as writing a morse (as in code) function that would blink an LED to read out particular register contents. At non-critical time, of course.

Dennis