As the kernel/distro maintainer for a commercial (focused) linux distribution, I have always been in trouble choosing which kernel to use and evaluate (as well as other core parts like C library). Latest kernels (>=2.6.32.X) have too much issues for us to use them unless in very specific scenarios. Those issues might not relate to the kernel directly (for example, we do have to support old mISDN releases), but the whole system integration is at a stake [I remember a simple iptables formatting change broke all of our reporting system, as well as frequent crashes on Xen due to heavy memory/IO contention].
We cannot afford a full regression test. We need to rely on what kernel guys tell us - it's a "longterm" and "stable" release. This means we can expect patches for severe problems to be applied, without compromising the system as a whole. We don't hack the kernel ourselves, nor have the means and knowledge to do so. Nor can we afford to be a "debian" or a "redhat" - effort spent extracting, forward/backporting patches is just too high for a company like mine.
In case you're wondering, yes we do comply to all licensing terms in all our components, and often we do contribute back (although our contributions are rarely accepted mainstream).
2 years for a long term kernel is a killer. 2 years for developing a full-fledged product is just too narrow - a 5-year support would be ideal here.
Things must move on, but for small companies (<30 employees) doing linux, tracking all kernel changes and adapting them (not all of those changes are kernel-mode specific, they require userspace adaptation) is a no-go.
Remember official Xen Dom0 support was stuck to 2.6.18.