Rumors have been swirling for a while that Apple is unhappy with Intel's performance in regards to their CPUs. After dropping the PowerPC architecture in 2005, Apple then switched to Intel units for its PC range. The introduction of the iPhone 4 changed that, with Apple deciding to make their own chips in-house and then using them in the iPhone and iPad.
MacBidouille, a French Apple rumors site, is reporting (via MacRumors) that Apple is now actively developing ARM-based desktop and laptop Macs using knowledge gained from the production of the chips used in the iPhone and iPad. According to a reliable source, Apple is testing an ARM-based iMac with 4 to 8 64-bit processors running on four cores, a Mac Mini with 4 64-bit processors across four cores and a 13-inch laptop with the same specs as the iMac.
The machines are, according to MacBidouille, well into the developmental stage and include updated keyboards that include a large trackpad. This is inline with the introduction of iOS-style features in OS X which can be accessed via a trackpad but not a mouse.
While the report claims the machines are developed and could possibly be ready for an announcement but Apple may be unsure about whether releasing such machines is a good idea. Intel is a trusted partner and releasing a machine that directly competes with their technology could cause Apple more grief than they want.