is there a noticable difference between ddr and ddr2 memory?

Answer 1

Uhm Shrimps... lower clock speed? DDR2 has much faster clock speeds. Officially, DDR tops off at 400 MHz, but it has known to go to 533. DDR2 tops of at 667 MHz, but it can be clocked to insane speeds of over 1000 MHz.
So yes, there is a HUGE performance difference. Originally when DDR2 was introduced it was no big thing but now it is. When DDR3 will get lower latencies it'll beat DDR2.

Answer 2

more pins, lower clock speed