If you're using the recently released unibody models of the MacBook, MacBook Pro, or MacBook Air, there are a number of firmware updates now available from Apple.
The EFI Firmware Update improves stability for each of the models and, at least for the MacBook, addresses problems with sleep-wake, USB, and device compatibility. I say, "at least for the MacBook" because Software Update on my Mac added that last bit; the descriptions on Apple's site restrict themselves to grunting "Update make Mac better." The updates are available via Software Update or as separate downloads for the MacBook [1] (1.8 MB), MacBook Pro [2] (1.9 MB), and MacBook Air [3] (2.4 MB) at Apple's Support Downloads site.
The SMC Firmware Update for each of the three models improves the sensing and accuracy of the MagSafe Power Adapter light. For the MacBook and MacBook Pro, it also improves the sensing and accuracy of the battery charge indicator lights. Find the 550K updates for the MacBook [4], MacBook Pro [5], and MacBook Air [6] at Apple's Support Downloads site or via Software Update.
These being firmware updates, be careful when installing. Apple has separate help articles for installing the EFI Firmware Update [7] and SMC Firmware Updates [8].
[1]: http://support.apple.com/downloads/MacBook_EFI_Firmware_Update_1_3
[2]: http://support.apple.com/downloads/MacBook_Pro_EFI_Firmware_Update_1_6
[3]: http://support.apple.com/downloads/MacBook_Air_EFI_Firmware_Update_1_1
[4]: http://support.apple.com/downloads/MacBook_SMC_Firmware_Update_1_2
[5]: http://support.apple.com/downloads/MacBook_Pro_15_inch_SMC_Firmware_Update_1_2
[6]: http://support.apple.com/downloads/MacBook_Air_SMC_Firmware_Update_1_1
[7]: http://support.apple.com/kb/HT3260
[8]: http://support.apple.com/kb/HT2368