Not exactly brand new tech...
Heat assisted recording tech has been used in magneto-optical storage before. I believe this is the tech used in Minidisc's, which was why they were rewritable (and later on, how they shoved 1GB of data onto 330MB disks with HiMD). In Minidisc drives the laser you saw at the bottom was not for burning to the disk, rather it just was for heating, it was the magnetic head above that did the actual writing.
Of course, this being applied to hard disks is new, and developing a head that has the required performance for disk speeds is no mean feat, so kudos to TDK for the work!
And in answer to Sir Runcible Spoon, it will improve performance, but as a side effect. The denser the platters are, the more bits will pass across the head per unit length. At the same speed, you will get more bits flying past the head for denser media, hence faster read/write speeds.
Now how much faster I'm not sure, hard disks are being specialised for large, slow storage. The "fast disk" area is increasingly being SSD based, with tiered storage systems. For example, I'm considering using http://bcache.evilpiepirate.org/ for ssd->HD caching of R/W IOPS.