I wasn't aware the 8300 did an automatic defrag. I know there's a way to do one, though, through the front panel. My original hard drive was a 160GB Maxtor and there was never an issue with performance. The drive died a few weeks ago after almost 10 years of flawless performance and I replaced it with a 320GB Western Digital IDE drive.
I've never heard of that one before. I think defragging drives is very overrated and unnecessary. With current file systems, such as NTFS for Windows, for example, it's completely a waste of time. I suspect the Seagate drives in the NB 3 would be the same.