In fact, I think the acquisition would have been in $50 mil range simply because VCs otherwise won't allow the sale. If they raise $2.5 mil at say $5-7.5 mil post money valuation, then for making 10x VCs would only say yes to an offer of $50-75 mil.
VCs may not have had a say - which has become more common, esp after only a single round.
Rackspace don't really do inflated acquisitions - they paid $18M for Slicehost and Jungledisk (combined). Cloudkick raised $2M back in April, so you would think that the price would be more around $15-20M.
Either way, congratulations to the team, RS and to YC. CK is a great product.