As a RHEL customer with 1500 deployed boxes I've had a fair bit of trouble with EPEL. The packages are managed to haphazardly. Some stuff gets pulled out of Fedora at the latest version, some gets old versions and some get left out. EPEL also doesn't play nice with other third party RHEL repos that have more history behind them. The packages also do not tag themselves as being EPEL in the package name. The package release gets tag'd with el5 and the Vendor is left at Fedora Project. I know where I got the various packages because there in carefully separated local repo's, but EPEL not claiming any of the packages needs to be fixed. They are not supported by redhat and should thus not carry the .el5 tag at the end of the release.
I finally just pulled all the EPEL stuff off my network and rolled my own straight out of Fedora for anything I need not already provided by RHEL5.
And for the record a 2 year release cycle for our OS would be a problem for us. It takes 4 months to just deploy all our boxes (they are scattered in groups of 10 all over the US with a few in Korea). We'd probably end up skipping every other release if they come to fast, but that has it's own issues.