Preparing microcontroller circuits, aside from the tiniest (8- and maybe 14-pin) ones, and lowest frequency (Tcyc > 1.25 microsecond) and sometimes even those, on a solderless breadboard is a total mistake. First of all, if you read the spec's, not only for microcontroller but also for other components, of which the solderless breadboard is one, you'll find that there's a significant capacitance between adjacent contact rows. This can often lead to very objectionable crosstalk, unreliable crystal oscillator, spurious interrupts, unanticipated resets, etc.

Further, because of the very nature of the solderless breadboard, leads are long, voltage distribution is often vastly poorer than desired, and high-frequency, high-impedance inputs are VERY susceptible to interference as well as crosstalk.

The only thing that works fairly well on a solderless breadboard is power supply bypass, if you're smart enough to include it.

The worst thing, of course, is that, at best, the connections are intermittent. Depending on whether you've carefully routed the wires and cut them to precise length or whether you've "air-wired" many of the connections, if you examine the signals with an oscilloscope, you'll see noise, Noise, NOISE, some of which is sufficiently low in impedance to cause unpredictable operation. Of course, the worst thing about solderless breadboards is that the circuit changes every time you touch it, or even when you just move it.

Much better, and thought by some, myself included, to be better than 2-layer circuit boards, is wire-wrapping. It allows reuse of all the components, easy bypass with a good wire-wrap board, excellent power-supply distribution surpassed only by multilayer PCB's with dedicated contiguous-pour supply layers, and absolutely minimal signal path lengths. Moreover, the intermittency of solderless breadboards is gone, the bypass cap's are in immediate contact with both the supply pins of each IC and the Gnd plane, and power-to-ground noise is minimized. Further, there's no manufacturing delay, aside from a couple of hours' time actually placing the sockets and components. Some wire-wrap boards even provide the sockets. Think about it!

RE