> seriously, when you scroll through a 10,000 email folder in moments
Err, no. Scrolling through 10k emails is a UX disaster. There's a reason why Search exists, and it's this use case. If your email is properly categorized, you rarely end up with folders that large anyway.
I've yet to see anyone handle email categorization and filtering anywhere close to as sanely as Gmail, and I seem to try everything about once a year, get pissed that nobody else can figure it out, and go right back to Gmail. It's especially important to someone like me who's on dozens of open source mailing lists and needs to cross-correlate conversations between lists ("[List Y] Hey I need to update X to make Y work again." "Go talk to someone on list X and file a bug on X's tracker..." "[Bugtracker X] Bug for making Y work again" is an incredibly common email workflow in OSS-land).
My biggest pain in email these days is that Gmail hasn't implemented any kind of smart filter for idiots that can't figure out their own email address - (namely, people signing up for email lists and using services thinking they have my email address... I keep getting incredibly absurd why-the-hell-are-you-even-emailing-this email including medical records, police reports, travel documents, confidential legal communications, etc. from people who share my particular first-letter-last-name pair).