I guess my responses are:
1. Zendesk We needed a good system, not really outsourcing of support. So, we do our support in-house but we use the Zendesk SaaS system to manage it.
2. GetSatisfaction As above.
3. SendGrid Email deliverability was not a piece of expertise we had in-house, especially when we were 2-3 people. Now we're 10-ish, our sysadmin guys STILL don't want to do this stuff.
4. MailChimp Hand-coding HTML emails more than once was boring.
5. Apigee This is something we were on the fence about. The metrics visualization probably swung it.
6. String No-brainer :)
7. ExpressionEngine Still a bit of friction in the decision between self-coding or using EE. But it's the 'annoying' stuff that swings it like plugin availability for new functionality, rather than do-it-yourself.
8. Chartbeat Couldn't do this ourselves.
9. Mint Could do this ourselves, too cheap to bother.
10. PivotalTracker As above.
11. Salesforce Industry standard, makes sense to outsiders, reliable.
12. RightSignature Awesome. No point building ourselves. Legal worries too if we did.
13. Gotomeeting Yeah no way we want to build this.
14. Xero The non-enterprise stuff we do is billed through our own app. But Xero makes sense for invoicing and proper accounts. Risk is, if you build it yourself, you need to know GAAP inside-and-out AND still it's a concern for outside auditors I think.
15. Dropbox Yeah no way.
BONUS: Office Glico Well, we could get an intern to go to the mom&pop store every week. But no.