There's a new glibc in the Testing repository, version 2.3.3 (pulled from gnu's CVS). It includes the Native POSIX Thread Library (NPTL), as well as the kernel headers from 2.6.
This means that people running a 2.4.x kernel cannot use this glibc, or else they'll face the dreaded "FATAL: Kernel too old" message after upgrading.
If you'd like to use the testing repository, it is here:
Server = ftp://ftp.archlinux.org/testing