Another thing to keep in mind, because we've got Intel processors in our Macs now, it's a lot easier to upgrade those, too, WITHOUT having to buy from a custom CPU upgrading company. I read a great article about how when Intel introduced the new Clovertown Xeon chips, these guys just popped them in their Mac Pro, lickity split. As easy as driving down to a PC shop and picking them up, just like any PC user. Now, I don't mean to be simplifying the process or anything, but it's pretty cool to be able to do that down the road now. Standards can be a good thing, when the stuff you use is part of the standard.
http://www.hardmac.com/articles/70/ This is the CPU upgrade article.
http://www.hardmac.com/articles/70/ This is the CPU upgrade article.