I find that debians support cycle for stable is troublesome for long lived servers, as the support lifetime is unknown, other than it's a year past the release date of the next stable version. That means that the minimum lifetime before needing to recheck everything for stability is one year plus however long until they release a new stable.
In contrast, ubuntu is at 5yr support for their longterm releases, with a known 2 year cycle in-between. Which means that even if you install in the worst possible time in the cycle, a new install will be supported for three years.
I really like those extra two years of security updates.
(edit for iPad text entry)
Debian is great for one or two machines, but based on my experience with it I can't imagine using it for 10,000 boxes
As for requiring a very specific configuration, most of the time that is only in one corner of the machine. I would even hazard that if you have strict requirements for every facet of the machine that differ from the defaults (and this machine is not handling super-sensitive information, super-high performance jobs, or publicly accessible) then you are doing it wrong.
(I assume we're not talking desktops here.)