I see it this way. If you are fully rooted and want to try out a 2.2 leak, or an alpha, beta, whatever..., go for it. You can always go back using nand restore. You can try out new roms, test them out for others, basically its up to you. I agree with Ken that the .3 release most likely will be the final but even if it isn't, it was well worth installing the roms based off of it. As well as the many froyo releases out last week
Now if you are not rooted, then absolutely I would wait for the final Shipped Sprint so you dont have issues moving from .1 or .3. Not to say you will be but the advise should be heeded by the non-rooted.