I think Apple should update their computers once every 5 years.
And you would buy today a 4 year old machine for the price of the latest hardware out there? $2500+ for a machine with 2x2.66GHz dual cores? An iMac for $2000 outperforms that one and it comes with a great 27" screen.
You have to think what you would get when you buy a new Mac for your money, rather then upgrading your machine at every 166MHz processor speed bump. Apple however is not really good at providing the latest technology to it's customers. Putting in sockets for CPUs is a good idea if they can't keep up updating there machines with every 166MHz bump in CPU speed. If they'd love there customers that much, they'd do. But as these things are rock solid and are outdated long before they stop working, you'd not make enough money of it. Intel changes it's socket every 12-24 month anyways, so it doesn't make sense. Like the first Minis, you can't put newer Core 2 or i-Series CPUs in, even if they have sockets, so you're forced to buy a new one if you want a faster processor. Apple might not have got that memo.
I bought my first Mini, even if I would have expected at least a i5 machine, not because of the price, but because they state to build the best computers in the world. Apples hardware is outdated on release date, and nearly always is, but the build quality and the software legitimate the price. The extra you pay for the

should include the engineering effort to put a i5 in there, that's what an engineering driven company does, that's what we pay them for. There are 2.5" 750GB drives floating arount for a couple of month which fit the Mini, MB and MBP, Apple doesn't seem to be able to offer them. For the price they charge you for a BTO hard drive upgrade, they could order them from NewEgg and still make profit with it. I predict the same for 3TB desktop drives in the iMacs and Mac Pros when they hit the streets later this year, technically they work without any modification to the software or production process of the Macs.
That applies to the Mac Pro as well, but as this things are faster then recent consumer i7 machines anyways, no one cares that much. Six-core Xeons use the same Socket and fit in there plug and play, the demand would not be that huge so Apple would run into any kind of shortage on that chip, as these machines will be >$3000 anyways. These things are build on demand, it would be just getting the CPUs off another shelf then the quad-cores.
Doesn't make any sense at all, but sure, why not. iPhone 4 and iPad are money making machines, who needs Macs? If the 2011 line up is the same as this years with some minor MHz bump, it may be that there will come some Über-Microsoft company and take over the PC sector. That may be even the GNU/Linux community, if they radically improve their UI and usability. Technically, they're ready to go since a long time. The system itself is always the first to support new core technologies. They adapt to everything, if you hook a display up your toaster or coffee maker, it runs Ubuntu. Even the iPhone 3G runs Android. If you take away the OS, only thing remains is an unibody aluminum enclosure. ASUS and Dell might be able to build similar things as well, so do LianLi and Chieftech for desktop cases.
If you still use your 2006 Mac Pro that's fine, it's maybe as fast as a recent iMac or MBP (depends whether it's duo or quad), and that's the fastest Apple offers today in it's consumer line up. Newer Mac Pros blow it away, though.