this week i upgraded my glibc to 2.3.1 on a redhat 6.2 machine. this
isn't strictly a lfs question, but i think this is where somebody would
more likely know.
i was sick of not being able to run some newer software because of the
old glibc, 2.0.X? something, that it came with. i first tried 2.3.2, and
most stuff still worked, but i was getting problems compiling almost
anything. i restored a backup then tried 2.2.5, rebooted and almost
nothing would work. 2.3.1 works with almost everything. i just had
to recompile an old version of wine that i need for eudora.
anyway, i'm having trouble compiling some things that i didn't have
trouble with before. like i've compiled transcode dozens of times,
and now i can't. xvid wouldn't compile either. i restored my old
backup to a different partition, and compiled transcode, and copied
it to my newer system, and it works, so i'm looking for suggestions of
maybe what else i need to compile, upgrade or recompile to get things
working smoothly. besides what i had to upgrade to get glibc to compile.

Did you make sure *everything* the glibc documentation says is needed was updated? Compiler, make, etc?

Updating glibc isn't quite as simple as updating other packages, and the guidance in the documentation should be followed. For example, did you install in runlevel 1?