Here's a tool that I use for learning about basic electronic circuits (I'm not an EE grad). Putting together simple (and some advanced/complex) circuits, analyzing those circuits, simulating those circuits.
Well what's good about it is it can emulate PICs and soon Stamps, still no AVRs though.
Its not free software though, one has to shell out 19USD for a academic license but, there is a free evaluation version. Product maturity (?), well it still crashes on me from time to time. Learning curve, is not that high, just put devices then wire them. If it doesn't work and one knows what he/she is doing, one can find the fix to the problem easily but, for a noob (like me) finding those problems will take time. It won't tell you what you did wrong.
BTW, I'm not, in any way, connected to the creators of VBB. Maybe someone will find VBB useful too.