Western Digital announced the introduction of new drives today, these ones touting a very high density in 3.5" form factors. The Caviar series will be getting a boost from the Scorpio series in terms of density, with new 320GB per platter drives. For Western Digital products, this means they could offer 1TB units with only three platters, and along with higher density comes faster read and write rates.
The new Caviars are already available, and will have various iterations for all portions of their markets, from enterprise on down to desktop. The higher-density platters are from the same design as the Scorpios that were released in October of last year. You can read the full press release at Western Digital's site. There's no mention yet of what capacity drives they will be offering with this new technology, though most likely it will be 3 or 4 platter design.