[Update: 07Sep2007 - see the comments below about additional information about where to find sworldswaf.dll files and which one to use where.]
I tried to use the FME 4.1 SWAF interface today and ran into a problem where the FME clients (eg., Universal Viewer) could not recognize any of the data dictionary information queued up in Smallworld for export to FME. I contacted GE Help Desk and they were very quick (on the order of minutes) to send me a new sworldswaf.dll file that must be copied into the FME root folder (eg., c:\program files\fme). This fixed the problem with the FME 4.1 interface but then introduced the problem for the FME 4.0 SWAF interface. Not that big a deal unless you are running two versions of SWAF with the same FME clients.
Interesting notes about the DLL versions. The FME 4.1 documentation says that you need to be running FME 2006 GB build 2651 at a minimum with version 22.214.171.124 of sworldswaf.dll. The version of the DLL that shipped with my version of FME build 2651 was 126.96.36.199. Either the documentation has a typo or Safe Software does not have the latest version of the DLL. Anyways, the version of the DLL that the GE Help Desk sent me was 188.8.131.52 (that's right, it seems like an earlier version number). Apparently this DLL is still too new to have made it onto either GE or Safe Software's web sites. You will need to log a case with the GE Help Desk to get the correct DLL.
On a related note: One of my Smallworld-FME presentations was accepted to the 2007 Americas Smallworld Users Conference in Colorado this year. I hope to see alot of you there. More about that later.