What prompts my question is this post from Jeff Atwood, and this post from Dare Obasanjo. It seems to me that there might be at least a few areas where third-party functionality is a better idea than custom code.
For example, should logging always be third-party? How about encryption? Or search?
I'm looking forward to everyone's feedback on this.
Edit: This question assumes that logging, encryption, and/or search isn't your core business.
Encryption should be third party most of the times, ...unless you're in the business of selling encryption systems.
Which is pretty much Mr. Atwood his point as I understood it, your core busines shouldn't be third party, so there's probably nothing that should always be third party...