I found 0 performance difference between a 5400RPM drive compared to a 5200RPM found in the older 750GB and current 1TB drives. However, I did find a pretty huge difference when it came to comparing with the 7200RPM drive.
The advanced format does improve performance but it does not give you any more space. I don't know why they say it does. My 1TB is still 931GB, same with a non advanced format drive.
I've actually went through 4 Advanced Format drives. I've only returned the 640GB and 750GB. The other 2 drives, I have right now. Both are 1TB 5200RPM drives. One is in the iMac, doing a RAID-0 with a 1.5TB internal drive. The other is in the MacBook Pro currently.
For me, it's more about not having enough space then drives being defective. Like I said, I only noticed the 640GB drive to be extremely slow for some reason. The others are fine.
And yes, 1TB in a laptop is barely enough for me. I have 30GB of free space left on the OSX Partition of 880GB and 1.2 GB left on the Windows Vista partition of 120GB currently.