I had this thought after looking at a thread on an oscilloscope made from an arduino, and finally decided to mention it. Basically, I'd think an oscilloscope and frequency generator are the harder parts of an electronics lab to get, since the oscilloscope at least is rather expensive, and the freq generator probably similar. Fortunately, in the amateur realm, you don't need a whole lot, and as the arduinoscope shows, the level needed is hardly professional quality, though I'd imagine that's certainly possible with work and money.
Something I saw though was that the arduino can probably do some multimeter functions as well, with some outside help, and a few other things can be mounted on the same board, though probably separate for the sake of isolating them. So, the ArduinoLab concept is to build an arduino based "lab" containing all of the major devices you might need for electronics work, built into one package. Here's what I was seeing:
An Arduino, probably one of the bigger ones, would be mated to one of the LCD screen shields. This is the core.
An Arduinoscope variant would display on the screen in scope mode.
A multimeter would be in there, again using the screen for display, and probably with quite a bit more function than a normal MM.
A frequency generator, possibly run by the Arduino, but might actually be separate, with the Arduino tapping it to show information on what you're doing.
A power supply would probably be isolated completely, but that's not too much trouble. It would be a variable voltage regulator and potentiometer with a three digit LED, since you'd probably max it out at 12 or 24 volts. While the other stuff would use the Arduino more, I'm thinking you'd want to keep this isolated due to the larger potential voltages, so some way would need to be found to set up a reader so the LED display can show what you're getting, down to a tenth of a volt.
I'm thinking some sort of logic probe/serial monitor might be useful, with the serial simply showing a bunch of bits at a time. Not sure how useful something like that would be though. I'm sure some other people might think of interesting things to use, too. It would also need a decent battery, say an extended version of the power shields.
The real fun would be that using something like a Mega would allow multiple readings of all sorts of stuff. You could monitor several points in a circuit to see if all of them are working right at the same time.
Would something like this be of interest? With all the stuff you'd need, I can't see it being a whole lot less than used equipment, but it's a fun project and provides usability that's hard to find in one place.
Any thoughts?