You can definitely use the FT230X to communicate with & reprogram an ATMega; as others have said there's no DTR on the chip but AVRDude pulses RTS so just tie it the same way and all works well.
I ordered a MicroFTX (http://jim.sh/ftx/
) to evaluate the chip and it's been working reliably on various breadboarded designs for a few weeks now.
Regarding the availability -- early versions of the X chips have a USB bug that's supposedly been resolved with the new Rev D chips that are just coming out. I actually got an email from Mouser on Friday that the chips I ordered in October should be shipping the 16th; I just checked DigiKey and they say they'll have them on the 13th.