I haven't had a helpful TAC engineer in something like 5 years, and then only because we'd spent hours with their low-level filter people, correcting the SQL statements they were attempting to run over their remote session. They ended up replacing most of the hardware in the server (which was a nightmare in and of itself... and took far more than 24 hours) only after having us wipe and rebuild it from scratch, and that system still doesn't operate quite right. TAC is the thing that SmartNet is LEAST useful for... my only purpose in having it is to get software updates in a legally compliant fashion.
I'll grant you that when I started in networking 10 years ago, I was amazed by TAC. Since then, either I've improved or they have declined.