If you want to convert FBX files to OBJ format, you may use free Autodesk FBX Converter.
Most of library i seen here are very old fashioned furnitures or more US-Goods
It's funny, some European users of Sweet Home 3D criticize the US style of some furniture, and American users criticize their European style! 
About being old-fashioned or not, don't forget that the furniture libraries available on sweethome3D.com were designed by contributors and are freely redistributable under CC-BY license or the like. When I started to program this software, I never thought we could reach 1200 pieces one day! If you want more fashionable stuff, feel free to contribute yourself.
About importing home designs from Revit, maybe it will be soon possible through IFC files which support in Sweet Home 3D has been in the works for a while. Stay tuned!
----------------------------------------
Emmanuel Puybaret, Sweet Home 3D creator
