I don't know if this has been mentioned, but Vista style file copying should be added to the Mac OS X.
In Vista, when copying over any file with the same file name as one that already exists, a dialog box pops up asking if you want to replace or rename the copy so you can have them both.
While not a common occurrence, it's one of those little features that is greatly appreciated when the situation does happen.
Furthermore, when replacing data that already exists, the amount remaining to be transferred does not change. For example, if you copy over 20GB of files, and 5GB of that data already exists (and you choose to keep the existing data, and not replace the ones in the destination), the transfer window will still say it is transferring 20GB of data. Because of that, if only 18GB of space is available on the destination, even though the amount being transferred is only 15GB (because you chose to not replace the existing 5GB), you will get an error saying there is not enough free space.
This is bothersome when you have several hundred files, and it's easier to select all of them to transfer while wanting to not replace the existing ones in the destination rather than having to go through and transfer them individually or in batches that total less than the space available on the destination.
I don't know if that's a Windows feature, but it sure would be nice for the Mac OS to be smart enough to figure that out.
Edit: Like I said, it's definitely not a common occurrence, but I have personally come across these scenarios dozens of times and it always ends up being a lot more difficult than I feel it should be.