Flat out, it depends. I get something from Jeff, Gail, Lynn, the usual suspects, I will review it and test it, but I'll generally assume it's right. I get something from other sources, I'll try to vet it, get second opinions, do a bit more research, and then review it and test it. I don't think I've ever simply copied & pasted code from online to my production system, ever.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning