If You Want It Done Right, Use A Third Party
Third parties like the YUI and jQuery teams for example have huge user bases who field test and report bugs far more rigorously than any in-house QA regimen can ever hope to. And since the YUI and jQuery libraries are their respective teams’ core products, they do nothing but build, debug and maintain them full time, which is far more than any in-house team could hope to do. And if a dedicated in-house team is put together to focus strictly on a non-core product, then it will at a direct cost to the company. And what do you do when you need another library to answer another need? Build another team? That’s hardly a cost-effective solution.