The speed difference is just theoretical as yet. Today's drives are not using even full SATA bandwidth i.e. 150 mbps but SATA-2 is definitely the future. We will see cheaper and faster SATA-2 drives in future so if you are planning to buy a Motherboard then buy one with SATA-2 ports instead of SATA-1. You can use SATA-2 drives when they actually start using the full or at least a part of SATA-2 bandwidth. Till then just use SATA-1 drives. SATA-2 is backwards compatible so you'll face no problems in doing it.