I get accused of being very negative about Apple, but I'm not: I think Apple's Intel decision was the worst choice they could have made in reaction to IBM's failure to deliver on its promises, but I continue to recommend Macs to friends and colleagues.
What makes a Mac isn't the hardware, but the "user experience" - basically the combination of hardware, software, and the cachet many people see in owning a premium product instead of a run of the mill PC.
At the moment, therefore, I think Macs are still the right choice in situations where the alternative is to buy and use Wintel, simply because Apple's software is far better.
The other two factors, however, are history. First, x86 hardware is just that: x86 hardware, the quality and performance premiums that went with PPC are gone - figuratively in terms of personal differentiation (aka "fashion") because you can't tell a Dell from a Mac without a label, and physically because one of the numbers hidden in that 10-Q I quoted yesterday shows that Apple increased its warranty reserve by 31% per unit sold over the same period in which it converted from PPC to Intel.
Secondly, part of the Mac's appeal was based on the perception that it was a better, more secure, machine used by smarter, more successful, people. Now in that context a one third increase in warranty claims doesn't demonstrate strategic failure, but x86 hardware is just x86 hardware and if the MacTel decision leads to the loss of Apple's appeal as a fashion accessory it could be in real trouble.
For example, the iPod and related lines are "mission critical" for Apple, but while iPod and iTunes sales are thought to be still growing, the momentum has clearly gone out of the market with neither product meeting volume targets set last year. Why? In my opinion because these are fashion items, sold on the basis of the "cool" halo conferred by the Apple brand rather than on genuine competitive advantage - and the Mactel decision has, despite unusually intensive Apple advertising, started to dissipate that halo.
Ultimately such halos reflect product quality in use - an Armani suit really is better then the off the rack stuff you get at big retailers, but Apple's x86 hardware is just the same as everyone else's x86 hardware, and that's a problem.
In the context of PC security, for example, Apple used to get a lot of value from the reality that people buying Macs could pretty much forget about that whole PC "security" thing.
(Note that Mitre lists only 105 Windows/XP security vulnerabilities for the period but I don't know how that actually compares to Apple's experience because none of the counts involved, and certainly not Microsoft's, are excessively honest.)
Notice, however, that the key indicator here isn't how many patches they issued or how many vulnerabilities were reported, but the change in Apple's behavior with respect to those problems. In the PPC age, Apple took a legalistic approach to attackers, but a fairly relaxed approach to dealing with any actual problems found in the code: fixing the source for the next release, but producing downloadable patches only if the vulnerability drew a lot of publicity.
That's changed dramatically: now Apple responds to each new vulnerability with an emergency patch users are expected to install right away.
What happened? Simple: with x86 a vulnerability amounts to an exploit, with PPC most vulnerabilities are practically unexploitable - a phenomenon whose consequences you can see in the Solaris/SPARC world too where the popularity of Solaris for x86 has led Sun to introduce a slew of automated patch management tools that were previously unneeded.
So what's the bottom line? I still recommend MacOS X as a great Unix desktop: but now it's just about the software - the fashion appeal, the quality, performance, security and cost advantages, are all gone.