MacBooks not upgradable to Merom

A lot of people wanted to see a new MacBook Pro based on Intel's Core 2 Duo processor (code-name "Merom") at WWDC, but as I've said here before, it's just too soon. The MacBook Pro (15-inch) was announced less than five months ago - on February 14th and Apple doesn't want to make all their new MBP customers obsolete with a chip upgrade that soon. Not to mention the existing inventory of MBPs they'd be sacrificing.
Intel released the Core 2 Duo T7600 processor ("Merom" pictured left) on July 27 to replace the Core Duo T2600 ("Yonah" pictured right) found in the current MacBook and MacBook Pro. Core 2 Duo features 4MB of L2 Cache (compared to 2MB in the T2600) and is supposed to run cooler. Although Apple has been sampling Merom chips for a couple of months the processors won't be available in quantity until the second half of August, according to Intel.
Initial benchmarks comparing the T7600 and T2600 chips observed only a 12 percent improvement in Mobile Marks and a 7 percent jump in battery running time, but Mobile Marks are somewhat antiquated and may not be relevant to Mac users.

The good news (according to AnandTech) is that:

If you've got a 945GM or 945PM equipped notebook, then the Core 2 Duo should be a drop in replacement for your Core Duo processor.

(The MacBook Pro ships with an Intel 945PM chipset and the MacBook, iMac and Mac mini are based on the Intel 945GM chipset.)

The bad news is that although Merom is pin-compatible with Yonah you need a socket interface in order to upgrade to Merom. Both the MacBook and MacBook Pro have Ball Grid Array (BGA) interfaces so upgrading them to Merom is out of the question - unless you really like to solder. AnandTech continues:

If you've got a Core Duo notebook with a PGA Socket-M interface, all you should need is a BIOS update and a Core 2 Duo CPU to upgrade your notebook.  If you've got a BGA CPU, then you're unfortunately out of luck as desoldering 479 balls from your motherboard without damaging it isn't for the faint of heart.

One consolation is that the iMac and Mac mini have socketed interfaces making Merom upgrades possible - but doing so will void your warranty.