I use Dropbox and Pinboard and Instapaper. I still find myself emailing things to myself because whatever iPad app I'm using doesn't yet integrate to any of those but does have email.
Email also exists on all sorts of devices that don't support apps.
That said, nice job - the simplicity and UX is great.
I remember collecting links for years on del.icio.us before Yahoo decided to shut it down. Then I moved everything over (though it's nice that del.icio.us made it convenient to move my data over, it's still a hassle) to trunk.ly, but now they have been acquired by delicious.com and will be shutting down too. In the end, I find that email is more reliable and easier to search (searching on Gmail is pretty easy)
One way such a website could be useful is if it did the job of emailing me the stuff I collect (or some other similar solution) so that I'm still guaranteed to have my collection, but it's possible to browse it in a better interface on this website.
TL;DR - This is a well-done website, but I'll be hard-pressed to use it unless it also solves the reliability problem.
Also, rave for pinboard: It hits that spot for me of doing one thing, doing it well, and not trying to do any other goddamn thing for me. It is $10. I think it's worth it.