I believe this was a concern raised the first time they were trying to sell it, but a big worry for anyone considering purchasing Softfolio is probably what would happen when 37s no longer owns it.
It's sort of like their job board (http://jobs.37signals.com/). People like the job board because of the types of developers it attracts. Both companies and prospective employees value each others' skills and styles. If 37s didn't own that job board and sold it, it suddenly becomes 'just another job board'. Is it the same deal with Sortfolio? Anyway good luck to the potential buyers of Sortfolio. Hopefully they won't have wasted $480,000.
I think it would be useful to know how much traffic / new signups come from other 37s sites vs SEO or links from other sites. That won't give you the exact answer of "how can it fall once it's no longer a 37s product", but it's a start.
It's sort of like their job board (http://jobs.37signals.com/). People like the job board because of the types of developers it attracts. Both companies and prospective employees value each others' skills and styles. If 37s didn't own that job board and sold it, it suddenly becomes 'just another job board'. Is it the same deal with Sortfolio? Anyway good luck to the potential buyers of Sortfolio. Hopefully they won't have wasted $480,000.