It's up to you which way to go, and whether or not you have the budget for such an upgrade, or even the need.
I doubt that the regular MacBook's have the dual channel abilities, but is this really necessary on a laptop? Also, dual channel means that both memory banks store copies of the same data, so that the CPU can get data faster. If you ask me, this is a solution desperately seeking a problem. The problem isn't getting data from the RAM to the CPU, the problem is getting data from anywhere else on the computer, particularly the hard drive, to the RAM. The new PCI-E bus helps to address that for add-on cards, but we're still saddled with rather slow IDE/ATAPI and even SATA hard drives. So, even if you have dual channel memory, and you can get data from the RAM to CPU 2X faster, the CPU still has to wait for data to get from the hard drive or an add-on card to the RAM.
For my money, it's better to have 1.5-2GB of single channel memory compared to 1GB of dual channel memory. While slower, you can hold more data in RAM, meaning fewer instances of needing to get data from the hard drive are required, making for an overall faster system.
However, that is merely my personal opinion, based largely on my needs and experiences. Depending on what you use your system for, dual channel may provide some benefit to you that it wouldn't me. I would hit some of the hardware review sites, and read up on dual channel memory. What it's good for, what it's not so good for, and then decide if it seems right for you.
As I understand it, the MacBook and MacBook Pro both have two memory slots for RAM...
The Pro will run fine with either a single memory slot filled, or even with two unmatched memory sizes (such as a 512MB DIMM in one slot and a 1GB DIMM in the other).
However, if both slots are loaded with an equal amount of RAM (such as two 512MB DIMMs of the same type), you can take advantage of the system's 'dual-channel memory architecture' for an additional performance boost (both banks of SDRAM can be addressed at the same time, for greater memory throughput.
Is this true for the regular MacBook too? Should I upgrade my 2 512MB for 2 1GB chips? Or can I just get one 1 GB and add it to one of the slots, to have 1.5 gig total?