Their "business accounts" implementation is incredibly poor for people who already use Dropbox (ie the people to best please and most likely to spread the good word). For some bizarre reason they decide on this weird merge of one business account and one personal account. If you have more than one of either then tough luck. If you don't want your personal stuff and your business stuff co-mingled then tough luck too. If you want exceptionally confusing web pages with hostile flows, then they have you covered. (Yes, I just set up another one today and it was beyond painful.)
What they should have done is how Google etc handle it. You login with multiple accounts, have a selector between them and everything just works.