>>Seems to be a consensus that performance drops off a lot with > 5/6000 files but haven't seen any hard data.....
>
>Would you know exactly what kind of performance drop would occur?

One of our systems reads lots of data from trains and dumps it on a folder where it stays for some time before being overwritten, so we wrote an application to FTP said files and store it in our network (the other computer is in a different network that only allows FTP access) and put them in a 2 Tb HD for long term storage, which currently is 1 year. We put the files in sub-folders for year-month and each of this sub-folders have 25 thousand files and around 130 Gb, and we do not notice any slow down... except when we run 7Zip for the folders that are more than a year old... that takes around 36 hours to run! But for normal operations, like browsing the folders, locating and opening the files, even the FTP, which checks existence of files before transferring we do not see a performance issue.

HTH

[Update]

Forgot to add that we disable short file names support because is my understanding that this could really slow down, specially like in our case, where files have similar starting names.