I have no problems with my NAS and long file names. The one thing you *DO* need to be aware of, however, is that extended attributes don't fair quite as well. Mac OS X has an annoying tendency of adding extended attributes to the files. When these files are copied to the NAS, the copy process fails (I'm not 100% sure, but I believe that the Mac is actually checking to make sure the files have been copied correctly, sees the missing attributes and decides that the copy failed, even though the message is that you don't have rights to the disk, it is write-protected or full).
My solution, at the moment, is simply to remove the extended attributes with the "xattr -d attributename", where "attributename" is the actual name of the attribute you want to remove (for example "com.apple.finderinfo") before copying them and it works just fine. Mostly this is an issue for me when I buy digital movies and try to copy them up to the network.