I'd like to swap the hard drives of two Macbook Pros. One is a Core 2 duo model from 2010, the other a 2011 i5 model. Will this work? I just want to save time and not go through a lengthy data copying process.
Yes. In almost all cases, OS X software is hardware-agnostic (as long as the hardware comes from Apple).
Yes, as long as both machines have Intel processors in them then both hard disks are formatted with GUID partitioning. If one of the machines was older and had a Power PC processor in it then you'd need to reformat and partition that drive for the newer processor and partition scheme. In your case, swap away.
It would be best to check with Apple on both serial numbers. They can tell you if the part number for each drive is the same or whether the firmware on each drive is 100% correct for both models. Of course, most SATA drives are fine in any mac for general use, but you can get slowness or less than optimal speeds or sleep/wake issues if the firmware on the system and the drive are at odds with each other.
As long as you have a SATA hard drive, it doesn't matter what it is. You can also buy a SSD and replace your current one.