DailyTech has published an article about Intel's Socket P which will be part of Intel's Santa Rosa mobile platform.
"Socket P" will part of Intel’s next generation Santa Rosa mobile platform and will continue to be a pin-grid array based socket unlike the land-grid array based desktop processors. There will be no backwards compatibility with "Socket P," as it will be keyed differently than the current Socket M. Socket P processors will have pins A1 and A2 removed unlike pins A1 and B1 of current Socket M processors. Sacrificial "Corner Balls" will also be introduced with Socket P for greater differentiation with Socket M processors. Intel's guidance clearly states:
Not pin-compatible with Intel Core 2 Duo for Napa, or Intel Core Duo T2500.