Is there a copy and paste limit?

The maximum number of files in any one folder is 2.1 Billion but I guess you mean drag and drop i.e. copy files from one location to another volume, or do you mean selecting multiple files from multiple locations to then copy ? (If so I'm not sure what the maximum limit is)

In the days of Tiger and its predecessors, the Finder would choke up if you tried to copy over too many files and I usually did it in 2000-3000 batches at a time. If I was in a hurry, I either went and did it with the Unix cp command from Terminal or used *File Buddy*, neither of which balked. Another thing which could also drag the Finder down was if you stored too many files in a directory; after over 23,000-25,000, opening a window to that directory would take ages.

However, this seems to have been corrected with Leopard and I have at least copied over around 7000 files in one operation. Can it do 25,000? Don't know, haven't had to copy that many files at once. Just make sure both HD's have no errors that could slow things down (i.e., run Disk Utility's Repair Disk on both every so often).

Another thing: if you are in a hurry, make sure to connect the HD via Firewire instead of USB. Even FW400 will beat USB2 every time. And FW800 is someting awesome; Migration Assistant pumped over around 40GB from my old PBG4 to the MBP in about 20 minutes.