At last night's Flex 4 (aka Gumbo) Open Iteration Meeting Adobe announced that due to all the feedback from the community, they are going to push back the Flex 4 release date to 'early 2010' and also issue a further beta release later this year.
This is great news as it looks like the team will use the extra time to make the transition to the new Spark component set a lot easier, both in terms of the features it has and using it with the older Halo (Flex 3) components.
There still won't be full parity between Spark and Halo until the Flex 5 time frame, but Spark is much easier to work with at the 'skin' level, which is often where it's best to add value to your clients (after all, it's the only bit they see).
Having said that, Flex 4 is going to get pagination for datasets that doesn't need special server-side software like LCDS or BlazeDS, which is a major boost.
You can see all the other things discussed in the recording.