If you merely changed your hard drive and no other components, and your IDE hard drive wasn't 5 years old and 5400 RPM's etc., I have a hard time believing it. Also if you moved from say a 80gb hard drive to a 300gb Seagate drive, you'll notice a boost, newer Seagates (250gb+) are a pretty good transfer rate). Plus your 80gb was probably full, reducing the access time on the drive. A less full drive is going to perform faster. You may have seen an increase if your cache was 2mb on your old drive to 8mb+ on your new one and your benchmarking huge files, then yes.
You would really need to benchmark both drives using a program like HD Tach. On my set up, 1 of my Maxtor drives on SATA 150 put out around 70mb/sec. Once in RAID 0 with an identical drive I was reaching 105mb/sec. A 35mb/sec increase is a noticeable difference. However, as my drive gets more full and etc, access times slow down. Kind of like, why does my computer after a fresh reformat boot in 20 seconds, but after 12 months of acquiring more data on it it takes 45+ seconds.