Marina,
We have always viewed Eclipse Milestone builds as experimental/early-access software. In many cases API changes are incomplete and new bugs emerge between milestone releases that can be difficult for a MyEclipse3 user to discern as to whether the problem is MyEclipse related or a Eclipse 3 milestone problem. A company priority is to provide trial users the most positive evaluation experience as possible which at the present is based on MyEclipse 2.x. Thus, there are no plans to provide trial access to MyEclipse3 for the near future. Again that may change as the Eclipse3 milestones become more stable from a product developer and extension perspective.
Michael
MyEclipse Support