I have about a hundred or so. I've stopped keeping count. They take up three drawers in the TV armoir. The amount will go up pretty soon because my birthday is Wednesday (August 23) and I'm guaranteed a few DVDs as presents.
I guess there are no absolute rules. I tend to deal with box sets like this, though: If the set is just a "bundle" of DVDs (preferrably including covers) that are also released individually, I usually count every title. If not, I probably count the whole set as just one.
Count every title as one DVD. if you buy "Family Guy: Volume Three", count it as 1 title. if you buy "The Complete Indiana Jones Movie Collection" count it as three titles. Each movie or each TV season, counts as one
We need season sets of all DCOSs and all DCOMs on DVD! And Better Cover Art!