gtvr :
If I was buying one, and the difference between a SATA 2 MB and a SATA 3 one was 5 or 10 bucks, I'd do it.
Found my way to this thread on a quest to build my first system.
Buying sometime this week the ASUS M4A88TD-V. It's about $20 more than lesser boards by ASUS in the same theme that are USB2 and SATA2. It also got me the 128mb sideport memory so I don't need to buy a video card, but I'm not a gamer.
Also: most HDDs I've looked at are available in SATA2 or SATA3 for about the same price.
Some food for thought:
I have an idea of a crazy fast boot drive, but I only started learning about hardware a month ago. CompactFlash cards are IDE native. Grab a couple adapters and some fancy UDMA6 600x cards and you could smoke a consumer grade SSD. But that's way to expensive. The new CFast cards are native SATA and cost hundreds a gig for industrial applications (check out the brand addonics).
Realistically ($100), you could get 4x4GB CF cards UDMA4 250x and 4 adapters for about the same price/speed as a 16GB SSD. RAID 5 for security at the cost of capacity, or RAID 0 for kamakazi style. The 2 drawbacks are that it CF has a limited lifespan based on writes and that it is a silly idea anyway.
I can't help but remember the time my dad spent $160 on vacation for a 1GB SD card and I got one for $30 6 months later. My main problem with buying an SSD at this time is that too much of the price is just for the newness of the idea.
SSD is the future. Mechanical drives have mechanical limitations. Ask your mom or kid sister what an SSD is. The day they can answer that, they will become affordable. I'm probably going to RAID up some Caviar blacks or Samsung F3's and wait for the prices to drop.