The business model I'm following most closely resembles the now-defunct Contenture; Readability is similar but not identical. Obviously I have some additional technology secret sauce or there wouldn't be a project in it to satisfy university requirements.
To me the main failing of conventional tipjars is the requirement to manually tip the recipient. To my eyes Tipjoy was the first real twist on this -- that you could commit to tip before paying -- but otherwise it was the same as Flattr and the dozens of others that have come and gone in this space. Flattr's twist is OK, but I think imposes even more potential cognitive overhead in terms of "I really like this site, I need to find more articles to flattr".
I think that the Contenture / Readability / my-company-name-here model works better because it requires no thought on the part of the customer. Payments are divvied up automatically. No transaction cost ("Do I tip or not?") is imposed on the user.
Mind you, my most imposing business obstacle is getting a merchant account. Businesses which take money from party A and pay some portion to party B are basically viewed as kryptonite crossed with rat poison by the banking sector.
Fair enough, too -- such businesses have statistically high rates of complaints, failures and money laundering shenanigans.