I know I'm being picky here but shouldn't heart rate be an 8-bit int rather than a float? Resolution of 0.1bpm seems unnecessary and if it goes above 255 an alarm rather than a precise reading ought to suffice  Same goes for values below zero.

Do you have a datasheet, or even a real part number for this camera yet?

You don't need an arduino to do this, just a digital camera 

Couldn't you also map some 82C55's into the external bus? If you wanted to keep any serial interfaces free for other purposes, you could use as many of those as you have free address space and end up with more I/O than anyone could ever want

I can't see that being very interesting for the male...

Unless that male is Photonicinduction. "Let's crank 'er up on the variac til she pops!"

If that's all you want it to do, you don't even need to use a microcontroller. A long time ago I built a circuit from some project book the name of which escapes me, that flashed LEDs according to the peaks of different frequencies using a few op-amps and some discrete components. As I recall, it wasn't all that complicated, and a piss-load easier than writing code. Of course if you need to do any intelligent decision-making other than just blinking lights, ignore what I just said :p but don't throw a micro at a project that doesn't need one.

A few weeks ago I read (it could be on this forum) that the TO-220 could not have 100A through the pins, even though the mosfet was specified for that amount of current.

I wondered about that myself... having worked a fair bit on big-ass electrical installation jobs and seeing the size of conductors needed to handle 100A, I thought seeing TO-220 packaged parts being rated for hundreds of amps seemed a bit ridiculous!

http://www.amazon.co.uk/Forrest-Mims-Engineers-Notebook/dp/1878707035

I used to have a bunch of books by this author. Definitely worth a look

I once had the idea of tiling a wall with old ceramic PGA-package CPUs, with the gold lids on them. I still might, one day.

Hard to do unless:
1) You are made of money
2) You already have a fair size collection of these CPUs
3) Your household average height is that of the Yoda or hobbits

These processors are hard to come by nowadays. You can pay $20-30 each on ebay and they don't all look good, mostly because they are headed for gold extraction. I happen to be a collector. It's harder and harder to get those gold lids. If you want a pentium pro or other bad boys, be prepared to pay $40 each. I'd be interested in making a belt buckle with one of these if I know how to make belt buckles.

All very good points Just a beer-idea really... awesome but impractical/impossible. But there IS a lot of e-waste out there, and a lot of people who don't know what they have. The other killer is that my ambition often outstrips my patience. I'd get one wall of the shithouse done and give up 

I once had the idea of tiling a wall with old ceramic PGA-package CPUs, with the gold lids on them. I still might, one day.

Maybe try a Teensy 3.0? Give yourself a bit of extra processing power

By complete surprise, and hopefully not preceded by "of course I know what I'm doing" or "hey guys, watch this!" 

Seconded. I see a lot of those connectors in my work

As far as I know, code can only be executed from internal flash memory. For beginner-level projects you're probably not going to run out.

Looks useful... I would probably take the bait if it really CAN be programmed properly in an Arduino-style environment (I simply don't have the time to learn anything more complicated). Having that level of simplicity paired with absolute pissloads of RAM/CPU power would save me having to make a lot of compromises. I don't really mind it running something Linux-y in the background as long as I can still make it do my bidding with as much ease as one would with an Uno etc.