Can I use my Mac during a backup?
 

i know it's generally good practice to not have any running programs during backup.

But if I really have nothing to do, what would be the potential harm to the backup if i were to, say, browse the web, write in textedit, or watch a quicktime movie?

if the harm may be the older version of the document gets backed up instead of the slightly newer version, then i am perfectly ok with that. but if i could get a corrupt file on the backup, then may be i won't do it. for example, what if a particular file is being backed up while i do a "save" for that file?

If you're writing to a file as we are backing it up, the file can look larger than it really is, which can cause the backup drive to fill (or you could get an error).