When I switched from Red Hat (original, not RHEL) to Ubuntu as my main distro, it was exactly this dilemma that bothered me. I was not looking for an Enterprise release specifically, merely one that I would not have to upgrade every 6-9 months, but which would remain current enough that I could still get packages to compile.
Fedora became too volatile, and (I'm afraid), I was not in the market for paid support, which made RHEL unattractive to me.
I selected Ubuntu (then fairly new, I jumped on at Dapper), and have mainly stayed on LTS releases although I did put Jaunty on a netbook.
My experiences are that Enterprise or LTS releases have good and bad points.
If you remain too far behind the curve, it actually becomes quite difficult to add compile-from-source applications, but you do get good availability and stability. As my day-to-day system is a laptop which I used to plug in all sorts of miscellaneous hardware to try to get working (I was ahead of the releases for WiFi, 3G broadband, TV adapters, HomePlug adapters), I needed to be able to take what was currently being worked on, and try it. This became impossible if you fell too far behind the mainstream.
If, however, you follow the curve too closely, then for a period of time after an initial upgrade, you may have stability and functionality issues. Like many users, I had quite a challenging time when PulseAudio became the preferred sound system.
My answer is to remain on the previous LTS release until the new one is 3-6 months old. This allows you to remain fairly current, but avoid many of the teething troubles. I'm looking at Lucid on one of my systems, but will not switch from Hardy yet.
Of course, many enterprise systems will be installed for specific applications, rather than for general purpose use. For these, upgrade the system in line with the application. Once you have it stable, leave it for as long as you can (security updates excepted), and only consider an OS upgrade if the application requires it, or the OS drops out of support.
To all of the people who are complaining about major applications changing with upgrades, what the heck! Just put your favorite on *in addition* to the new one. They are likely to still be in the repository in most cases, and work as before, unless the package owner upgrades it significantly (I still rue the day that xmms became xmms2).