I think you should use a free plan if actively using the 'free' plan will eventually force the user to go to a paid plan. e.g. dropbox. If you just give your core product away for free then users will only switch if they need the extra features of the paid plan. You can still use 'free' for marketing, because total conversion rates with a free plan will probably be higher, just don't expect these 'free' customers to…
This way, people who don't bookmark very much can live with 1000, and people who eventually will use more than 1000 need to subscribe...
I think it's a very good plan if your product is structured in a way that a user will eventually hit the limit, but I think Dropbox was not a very good example. If I hit the limit, I'll just delete a few files I don't need. I see your point, though, and I think you're mostly right.