Flex 3 does work with LCDS, but you need to ensure that you
are using at
least Flex 3 Beta 2 and add fds.swc to your libs directory
to your locale/en_US when compiling Flex 3 apps that make use
of LCDS APIs.
There is a known issue with Flex 3 Library projects (i.e.
compc) and Flex
2 formatted swcs, like LCDS's fds.swc. This should be fixed
in the nightly
builds of Flex 3 which you can download from Labs: