I wish I'd known how much FUN it was :) If I had I would have started playing with this stuff much sooner!

I wish I had known that every math class I would ever take I would use again, and more than once, and I sure as hell wish I had paid a bit more attention.

I wish I had a lot of hands on experience programming and using FPGAs. They are the new wave of embedded system development and I have only basic class experience with them.

I wish I had been taught how to use all of the modules of Microcontrollers in classes before my boss expected me to use them all.

I sure as hell wish that my university's electrical engineering department started design classes before senior year.

I wished I'd had a clearer understanding of Fuse bits. I spent half my time early on terrified that I'd brick my mega32. Oh and ditto with regards to serial IO.

I think of loop as being the arduino's substutitue for main in C. So I declared some variables at the top of loop. Bad idea, they get re-initialized each time around the loop. Instead declare as globals before any subroutine. Not a big deal, but it took a few minutes to figure out what was happening.

I wish I'd known how useful a board vise and a really good soldering iron would be. My Panavise Jr and Aoyue soldering station cost < $100 together, but they've paid that back many times over by making it a lot more pleasant to build things.

You don't absolutely need them, but they're much much better than helping hands and $15 cheapo soldering irons.

I'm with Kortuk. I wish we'd started simple design classes before final year of university, but specifically I wish we'd gotten to use an Arduino board in my classes!

We used a specially configured board designed at University of Wollongong based on an old Motorola chip, all programmed in assembler via a monitoring application. Pain in the arse!

Of course, I look up the course content for digital design now and they're all using Atmel AVR chips. sigh

I also wish I had more time to tinker with 'em, 'cause that's the best way to learn!

I wish i had arduinos and "make things talk" when i was a kid. I would have automated everything!

The CAN bus communication scheme and CANOpen.

I have used the Arduino a fair bit and I wish I had known how difficult serial IO was on arbitrary pins. I eventually settled on a 3rd party library but it took weeks to get to that point and even then it was not rock-solid reliable.

One thing I wish I knew better is analog circuit theory. 1s and 0s are easy...hook pin 1 of device A to pin 2 of device B.

A second-order band-pass Butterworth multiple-feedback filter...not so much. And then you have to worry about the characteristics of the op-amp, like whether the capacitive load on the output combined with the output impedance of the op-amp creates a pole which makes the output oscillate.

Or let's say you want to send an audio signal to headphones. You must carefully choose a DC-blocking cap, because it will combine with the impedance of the headphones to form a single-pole low-pass filter. Pick the wrong cap and you will neuter the bass frequencies.

Similar to the accepted answer, I wish I had known about Arduino's sooner. There were some designs I was looking at doing around the house. I have no problem designing my own boards with uC's, but I just didn't want to pay for the PCB costs at the time and then mounting SMT chips. So, those projects fell by the way side. However, now that I know about Arduino and all the shields for it, I'm considering them once again.

I wish I would have known that I could get free samples from a lot of online stores. Then I wouldn't have been forced to choose which project to get started on based on cost. And I wouldn't have been afraid to buy components that I wasn't 100% sure I could get working.

I wish I'd known just how easy it is to make a BSD programmer and get started. That would have saved a lot of time tool hunting. Of course I also wish I would have had the Bus Pirate sooner :)

And I still wish I knew where to get more chips cheaply (including delivery).

What I wish many of my interns knew is how difficult and demoralising electronics can be. I see many non-engineer types try to add some flashing lights and sensors to a fashion project or something, not realising that they're heading for a debugging nightmare.

If I was to write a book on electronics, I'd do my best to scare people away in chapter 1. Anyone who was left would probably be able to put up with debugging.

Everything.

(Yeah, it's unrealistic)

(Also, better).