No limit. The reason to consider multiple accounts isn't because multiple accounts would put you in better graces with Google, its because if Google decides to ban one of your accounts, you still have the others.

Note that it is against Google's TOS to have more than one adsense account per person or entity. Note that you could have one, your wife could have one, each llc you create could have one, etc., and still abide by the TOS.