Never ever upgrade your glibc from anything other than an official RedHat RPM. There's no reason to do otherwise.
Now, RedHat's glibc (2.3) has worked fine for me. Sometimes, you'll need to preface a command with LD_ASSUME_KERNEL=2.2.5 so it'll use the old threading model, but that's hardly the worst thing in the world.
The only program that I've found which absolutely requires that preface is SimCity 3000 Unlimited.
For the record, a seg fault (aka, a core dump) usually occurs when your program attempts to access memory which it doesn't "own". If you screw up binary compatibility with a bad version of glibc, I would certainly expect to see lots and lots of seg faults.