I can't become a Thane of Riften even after I have stopped the skooma trade and bought the house. I also don't have the misc. objective to help out the people of the rift. If it helps, I started the means of stopping the skooma trade by talking to the Argonian who wants to be skooma-free. I did not do what she asked right away and did not do it until way after the main quest was completed. I also ended the civil war in the Empire's favor so Maven Black-Briar is now the Jarl of Riften. I brought what the Argonian wanted me to bring and told me about the skooma trade. I brought this to Maven's attention and completed it. She allowed me to buy a house in Riften, but not Thane-ship. It was then I had noticed that her dialogue did not bring up the five things to help the people. It also did not give me any dialogue choice to ask about it either. Hopefully this will help to identify the cause of this bug.
I've got the same problem, only on the ps3 version. I completed all of the skooma trade quets started by the argonian and was in conversation with Jarl Laila throughout the three part quest, I completed roughly 6 favours without any quest updates, and I have done countless bounties, where in whiterun and solitude the bounties ran out in riften they seem to repeat themselves. There was no dialouge option to become thane or buy a house.
Eventually I decided to complete the imperial quests and change Jarl's, I am now able to buy Honeyside house in riften but not become thane still, The Jarl Maven wont even open up a dialougue box with me, just keeps muttering about how the throne feels and how her new title suits her.