It's not as big a problem as it used to be, but it does still have a noticeable impact on battery life, and there is of course the storage issue.
Personally on a portable machine it doesn't make a whole lot of sense to me, although if you intend to use ALACs at home then it is probably the only easy-to-handle way of managing your library. I take the hard way to maintain an interlinked FLAC and MP3 library, and combined with some of iTunes' foibles it can be a freakin' nightmare, but I still find myself gravitating to the evil iTunes.