I've several directories (including a thumbdrive, /mnt/portmaster-download/ ) and weekly trudge through getting them more or less synchronized. However, the directories are so large that tools such as meld may be difficult to work with unless one is practiced. By chance I discovered today,
which if output in one xterm is concise and compact and informative enough that one could nonprogrammatically finish up any pending sync operations (and remove no-longer-needed package file) in less time than "usual" (although programatically it may be able to be done in a shorter time frame in the long run; I find it difficult though, since the number-and-name format of the package files don't readily accomodate finer-grained diffs...)
Code:
bsddiff /dir1 /dir2