We were sitting here slathering ourselves with aloe when we noticed that Consumer Reports has a nifty article on how to buy a humidifier. Yippie! Along with a warning about small tabletop models:

Consumer Reports tests show that manufacturer claims can be a poor guide to how well a humidifier will work. Several small tabletop models fell well short of their claimed output and might not raise the humidity to the desired level.

How to buy a humidifier [Consumer Reports]