Oh, the big blk....dat files at the top level of Bitcoin are now unused?
i'm not quite sure about that. If you upgraded to 0.8, then the .blk files
may be still used. Personally, I did a fresh blockchain download using 0.8, only keeping wallet.dat, and that leaves no blk files.
Not sure about on Mac, but the Linux version appears to create a levelDB index file, but keeps the old data structure (blk00x.dat). It then records all new blocks from there on using the levelDB scheme (138Mb data files).
I myself deleted the blk00x.dat files from the BDB days and re-synchonised the whole blockchain into the levelDB/0.8.x data layout, it saved me nearly 500 Mb disk space.