That 100K limit really sucks; I went to record a 10 second mp3 sample of a distortion I made, and trying to encode it to fit under 100KB destroyed the sound, defeating the purpose of it.

400MB don't seem too big for a databse, but the convenience for many people is being sacrificed for the site maintainer's convenience (no offense, I'd probably do the same). If you don't keep up with the ever-growing standards of computer memory space, then yeah, people will start to get annoyed.

It might be a bit of work, but you'd probably need some clean up program or limit to how much each person can attach. Maybe each person can have a manageable attachment account, just like an inbox with its size limit, so if its full, they must delete old attachments or something, I dunno...