A known bug in a Microsoft driver that controls USB 2.0 functions in the Core Duo 945 GM chipset can quickly drain notebook battery power once a USB 2.0 device is connected. Tom's Hardware uncovered this problem, which Microsoft has kept secret until they can find a fix, when reviewing several Intel Core Duo and ATi X1600 based notebooks. I am not sure if this affects the MacBook Pro, as their specifications page doesn't mention exactly what chipset is being used. Update: I wasn't thinking when I posted this, the issue is with an MS driver so the MacBook should be fine.
Our assessment and observations, coupled with extensive consultation with engineers familiar with Intel dual-core architecture, plus information we received today from Microsoft, have led us to conclude that an anomaly in the way the currently available version of the ICH7-M Southbridge communicates with Microsoft's ACPI driver, is at the heart of the power drain issue.