I'm curious - how did they wound up with per product user accounts in the first place? I would have imagined that as soon as you had >1 product, there would be a strong desire for single sign on - amongst othr things - to help cross selling, and to avoid multiple invoices.
37signals specializes in "punt to later" problem solving.
It's why I tear my hear out while using other company's basecamp installations and continually run into bizarre failure modes and lore-based work-arounds.
Accordingly, I think there's room for a 37signals that works. I'd sign up -- although I'd probably want to host it locally for our 3rd party partners to use -- so perhaps you should consider my opinion on web-hosted services slightly suspect.
- HTTP requests regularly fail. Page loads, resource loading, uploads -- all of them. Sometimes the page renders without any CSS, sometimes it doesn't load at all, and sometimes my uploads just timeout.
- UTF-8 causes ... issues. For instance, I've run into truncation of comments at UTF-8 characters.
I have to change my username and pass for my $7/month Backpack account just so 37s can bundle their underfeatured software? This sounds like a good excuse to learn a new web framework by building a Backpack clone.