First I have to say having more than 300 GB free on my laptop is great. I am not worried about running out of space anytime soon at least. That being said what about performance? I used Xbench for my testing and my test results were a little surprising. The Seagate 140 being the oldest drive it is not surprising it is also the slowest by far. The two newer drives the results are not quiet so clear.
While some of the early reports of performance on this drive indicate it should be faster than the 320 GB hard drive my testing is indicating that is not the case. The extra storage is beneficial and the performance is fairly close. Hopefully there is something that can be changed or configured to get additional performance out of the hard drive.
I would say the 500 GB is worth the price and the performance increase is good enough if you are using a hard drive that is more than a year old you will get a performance gain. If I find a way to increase performance I will make sure I post it.