At his GDC keynote, Phil Harrison revealed that PlayStation Home will be a free service going into beta starting April will a full scale launch in the fall. A Sony developer document says otherwise: there will be three phases to rollout of PlayStation Home. A closed beta will run from April to August with approximately 15,000 users, after which an additional 35,000 users will join the testing until October, when the service is expected to officially launch. Sony has not yet revealed how it will select users to be a part of its beta test.
Sony developers are aiming for the initial download to be under 500MB, and that subsequent downloads will "hopefully integrate a streaming method that makes [downloads] negligible." It's unclear at this point if other downloads (software updates, game demos and so on) will also make use of streaming or background downloads. Sony says that it plans to update Home on a weekly basis with content from first and third party publishers, non-game brands (likely to be ad sponsors) and users themselves. Additional items to customize Home Spaces and avatars will be "developed continually" in a flow of downloads and updates for users. Seasonal items for special events such as Christmas and Halloween will be made available for a limited time.