I recently wrote ncbi-blast-dbs gem (https://github.com/yeban/ncbi-blast-dbs) as a faster alternative to update_blastdb.pl.
It downloads database volumes in parallel on a multi-core machine, verifies md5 and extracts the volumes. The volumes are updated if a newer version is available on the server, or re-downloaded if corrupt. Aborted downloads are safely resumed.
Needs wget and md5sum, which are easily available on Linux and Mac.
sudo gem install ncbi-blast-dbs
ncbi-blast-dbs nt nr