John,
Clustering is definitely an option that must be taken with eyes wide open. The hardware and software requirements are different to stand-alone servers as you correctly pointed out. The training requirements are very different as the author pointed out, and must be undertaken before deploying such infrastructure. A "test rig from hell" should exist before any production deployment and should also be used for any change control, no matter how small, and this means more money replicating some of the hardware too. And no more "I'll just quickly apply this hotfix roll up and then bog off home to a quiet weekend" - everything must be checked and tested first.
But when it's all said and done, it can be sweet and resilient. I speak from experience, the first 9 months of active/active Exchange 2000 clustering (on MCS' recommendation mind you) was absolute hell - most of the problems were due to the hardware though. Once we had that ironed out, and re-deployed our active/active clusters into a supported configuration after SP1 came out with different supported configurations - read no active/active unless you got gobs of memory and limited the amount of concurrent users; I got to the point where each one Exchange Virtual server could happily run 5 months with no scheduled downtime, let alone unscheduled, and then it would only be failed over for SP or hotfix patches. I'd say, if done right from day one, it can be very very good indeed.
Cheers
Microsoft