You just can't seem to throw enough memory at Vista.
There have been a number of issues that Vista users have reported relating to copying and moving data, especially large numbers of files. Often there can be multiple errors at play making it difficult for Vista users to track down the problem, in fact very often there is little indication that file copy operations haven’t completed correctly. It’s only when the user checks the number of files in source and destination that they realize they have a problem.
While there are still other file handling problems in Vista, such as selecting large numbers of files (~1,500) cause serious spiking in memory usage (that is not released until reboot), hopefully one by one these issues will be addressed (SP1 maybe ... the current beta doesn't fix these issues). Maybe then Vista users can feel as confident handling their data as when they were XP users.