I'm certainly not a veteran or hard drive pro but to me the new Raptor just seems to be a natural progression from the previous model, with a doubling of capacity and cache and a switch to SATA 2, all of which you're perhaps paying for in the price anyway.
In terms of capacity, it may be that for people who use a Raptor for their startup drive the existing model is sufficient to hold the OS and applications, and for people looking for a drive to hold large volumes of data, other existing drives already on the market still offer more gigabytes per dollar whilst being similar enough in performance.
In terms of performance increase compared to the previous model, it seems to be upto 20% faster, nice but not ground breaking.
http://www.storagereview.com/articles/200601/WD1500ADFD_1.html