Season 3 has only last week started its broadcast run in the US. Considering that Season 2 aired around the same time in 2009 and only reached UK shores in Feb 2010, I would class it a good result if this new season were to appear on FX before next February.
That being said I have a suspicion that it may air during this autumn.
I did read somewhere that FX said we wouldn't have to wait too long for season 3. I was hoping that they might show it soon so we would be almost up to date. Like Sky did with Lost and 24. Oh well...here's hoping.