The Mossberg Solution -- The iMac Gets a Brain Transplant: "Our verdict: The brain transplant was a success. The two machines behaved almost identically in our tests. Compatibility is excellent. The new model easily handled all the major consumer software we threw at it. We never noticed the translator software, called Rosetta, and any slowdowns it imposed were so slight as to be indiscernible.
The new model was actually a little faster at a few of the tasks we tried, but nothing like the two to three times as fast that Apple claims. A mainstream user who didn't know what was under the hood couldn't tell the difference between them, even after using them for hours. It appears that the faster chip roughly balances out the translation effect.
Also, there are two drawbacks to the Intel-based iMac that we judged relatively unimportant to most users, but which could be crucial to some. It can't run old, pre-2001 Mac programs that were written for the old Mac operating system, called "Classic." And, even though it now uses the same processors that Windows machines do, the new iMac can't run Virtual PC, the Microsoft program that allows Macs to run Windows software. Microsoft is rewriting Virtual PC for the new Macs but won't be done until 2007. Some other company may bring out a way to run Windows stuff on the new Mac sooner than that. But, for now, it can't run Windows programs."
In fewer words: no discernible speed increase from the dual-core Intel on key apps such as Microsoft Office, for the immediate future, and some apps, including Virtual PC and AOL for the Mac (referenced elsewhere in the article) don't work. MacIntel, for now, is only a major upgrade if you're running all Apple software.