Judging from the price page, it doesn't actually look like this does that. The price tiers are still some combination of a fixed amount of storage and RAM per tier, with no mention of number of cores. Maybe this is because their EBS clone isn't ready, yet?
Cloud Block Storage is available through the limited availability program and it is billed as a separate add-on to Cloud Servers so you can have a flexible amount of additional storage to go with the fixed amount provided with each CPU/Memory instance type.
[edit added to answer the reply] This is not the dNAS solution available as part of our dedicated cloud platform offerings that can be connected to Cloud Servers over RackConnect -- it is an API accessible block storage solution that is part of our public cloud platform. [/end edit]
This seems to address the use case of wanting more storage for a given amount of memory, but not the reverse. You can't, say, get 16gigs of ram, without also getting a 620gig disk, nor can you control core count independently of the other variables, in contrast to (for example) EC2, where there are a variety of instance types with different tradeoffs in CPU and memory, and storage is effectively always added (and billed) separately. It's unfortunate that Rackspace isn't taking advantage of the opportunity this relaunch presents to increase the flexibility of their product.
As I remember rackspace is a cloud in the same sense that Linode is a cloud, but not in the same sense that Amazon is a cloud, ie. they've taken an existing vps product (Slicehost) and resold it under the 'cloud' brand rather then developing something new from the ground up as a cloud.
Per the blog post, Cloud Servers is no longer based upon an existing VPS product. Instead, it is based upon the OpenStack project that Rackspace started with NASA in 2010. http://en.wikipedia.org/wiki/OpenStack
