I would. I would pay $10 pm for the current pinboard service quite happily - and there are a bunch of things I hate about it!
I'd probably pay more for something that wasn't ugly as sin, had good support for team sharing, better historical browsing, etc.
On the other hand for a consumer web-mail service, or something like a DigitalOcean, I would definitely pay an amount like that.
For us - and I know for some other folk I've talked to about exactly this topic - things like delicious and pinboard are really important services. I've done a little bit of custdev around this since a "better pinboard/delicious" for my particular use case is something I'm interested in.
I may be atypical. I may not be part of a large enough market for a real business to be built around (only done a little bit of custdev ;-). I've no idea.
But I do know there are people willing to pay at least that much on a monthly basis. Coz I've got a smallish mailing list of 'em ;-)