Fast-forward 10 or 20 years. For decades, your life is on your
computer: recordings, family pictures, writings, address book,
recordings, and on and on.
Can you access them?
There's format. Some formats are open enough that there will always be working tools; , others aren't. Can you open your old MS Word documents? Can you play your .aac music files?
Also: organization. Will iPhoto still be around to read the file structure? Will your cloud storage provider still be in business? Where exactly are these files?
And: backup. We all struggle with that.
If you can read it in a text editor, you're good.
.txt, vanilla plain text ascii, is awesomely simple and solid. Suitable for journal entries, notes, computer code.
.html and .rtf are simple markup and pretty safe.
.pdf is probably ok, but less clearly so.
.doc* makes me nervous.
.wav and .aiff are uncompressed and totally
.mp3 has made the leap to universal/nearly open and I trust it to be readable indefinitely. Also mp3's keep metadata right in the file, so go ahead and edit it the way you like it; it'll survive.
.aac MUCH LESS CLEAR. I strongly suggest changing the default import settings in iTunes to convert to mp3 at highest quality.
.jpg's are compressed but, like mp3's,
.tiff is uncompressed and thus safe.
I prefer .png to .gif where possible.
Photoshop format I don't completely trust.