yeah i have to side with lejimster on that Aono, you probably would be defeating the point of having SSD's if you did it that way. Even though you're OS would be on the SSD's it would be held up by having to access the mechanical drive whenever you use one of the apps, which you'd probably notice more at start up. What you would probably be better doing is just using a mechanical drive as a storage drive for iso's, video's, mp3's etc.... and loading all of your apps onto a single/raided ssd.
I'd also advise strongly against 30GB drives aswell if i were honest, but that's me. Keep in mind that 3 raided 30Gb drives, whilst quite fast would still give you less than 90GB storage space which is'nt a lot these days keeping in mind that if you install games that a lot of them are dual layer (6GB+) lately + OS and Apps + any downloads + formatted space. you'll be through that it no time. Also keep in mind that if you raid drives together the raid volume will use the lowest volume drive in the raid, 2 64GB drives and 1 30GB drive will still only yield 90GB space. If however you bought 64GB as your first drive then that would be adequate enough to use as a boot drive and provide you with a good start point to think about raiding. 60/64GB is a good size to raid from since it is a common sized ssd and 2 or 3 raided ssd's of 60/64GB would still give you 120/128GB storage space which is still substantially more than 2 raided 30's at the cost of some slight performance loss (depending on the SSD's manufacturer, for example a fast 30GB vertex drive is as much as, if not more costly than, a 64GB samsung drive but the samsung drive is slightly slower) but would also probably save you quite a bit of money in the long term.