I filed my refund forms 843 for 2006 and 2007 in April 2008 for SSN and medicare which were withheld in error. I received a letter from the IRS asking me to give them 45 days to process my refund. However, I have received another letter from the IRS asking me to give them another 45 days to process my refund as they are kind of behind their work. I called the IRS office and was told that they are working on my refund. I then asked for interest to be added on as they are making money on my money and I am not, and they agreed to refund me plus interest. My question is, are they deliberately taking their time in processing my refund so that in the end I get frustrated and don't continue to ask for it?

You msut wait for IRS to process your FICA taxes refund. Yes, you will get interest as per the IRS rules.

There have been a LOT of Forms 843 submitted (I personally have submitted 18 Forms 843 for 14 clients in the past four months), so the IRS probably does have a backlog to work through.

Be patient!