We should be logging everything: with the technology we have, it makes no sense that conversations I have with people are remain only as memories unless I actively take steps to record them. What would it take to start logging audio?

The simplest, if you have a smartphone, would be just to set the phone to record all the time and change nothing else. Unfortunately, that doesn't sound so good: this is my Galaxy S II, recording from my pocket. You could add an external bluetooth microphone (wires would be annoying) but once you're buying extra hardware, maybe it makes more sense to get something specialized to limit power consumption and make things simple?

We could make a little box with a microphone, memory chip, and rechargeable battery. It could be very small, perhaps as a lapel pin. Each night you'd put it on a base station to recharge and offload the days recordings, uploading to some server. You could sell this as a service, where you upload everything and they text-to-speech, index, and archive it. Indexing and text-to-speech isn't currently that good, but once you're logging the audio you can improve it retroactively. It's probably already good enough for decent search.

The device itself is probably not so expensive; I think the main cost is storing the data. A day's recording in 14Kbps variable bitrate speex is 148MB, a year is 53GB. This is $2.90/month on Amazon S3 in bulk. It does compound (Y2 is 2x, Y3 is 3x) but storage is also getting cheaper, so it's not too bad. The speex codec is optimized for voice, but 14Kbps might not be good enough; I'd want tests.

Confidentiality would be an issue, but I'm not sure this is worse than email. We're mostly quite content to store our email on Google, Yahoo, and AOL's servers. Maybe make a little button so it's easy to turn off recording for sensitive topics.

Legality would also be an issue. My limited understanding of the law is that where this is restricted it's in wiretapping laws written originally for telephones. In most states you can record what you hear, though Massachusetts and ~10 others require the consent of all parties. A recent MA appeals court ruling, however, declared that:

the court found no probable cause supporting the wiretap charge, because the law requires a secret recording and the officers admitted that Glik had used his cell phone openly and in plain view to obtain the video and audio recording.

It's possible that if these devices were well known they would be easily recognized and so not secret. Perhaps a "this device is recording audio" label and a red LED would be enough? I'm also not sure what the cultural implications would be. Recording video in public is now not something you need to request to do; maybe people would just change their expectations of what would be recorded?