They are a good source of extra income, but i really wouldn't call it a reliable source of income, do not get me wrong, i know some campaigns pay quite well and the value could really be high for some users based on their country of residence, but that doesn't eliminate the 'uncertainty' around campaigns/bounties such as: quite a lot of bouties do not pay their participants, and for the ones who pay, they give out worthless stuff, as for signature campaigns, they can end quite abruptly, with no notice at all, now imagine being on the receiving end of any of these scenarios if you rely solely on one of this source of income.