It's either too early or too late, depending on how you look at it!

Like all bulbs Alliums need to be planted just after they've finished growth, which is in autumn.

Having said that you should be able to find pot-grown Alliums that will be coming into growth about now and these can certainly be planted out, although they will be a fair deal more expensive than the dry/dormant bulbs.

I saw pot grown alliums in the GC today, no dry bulbs at all.

If you already have the naked bulbs, they can go in now, but don't expect blooms until at least spring/summer of 2012, and maybe a year after that. Dealing with out of season planting is stressful for the bulb, but not as stressful as staying in storage for an extra year!