What does the Flex [Bindable] tag do?

This is probably overkill, but if you are really interested in what happens under the hood when you add the [Bindable] tag, I strongly recommend checking out Michael Labriola's Diving in the Data Binding Waters session from 360|Flex!San Jose. It is by far the most in-depth presentation on this subject that you will find.

To view it you'll need to download Adobe Media Player (which runs on Adobe Air). If you have problems subscribing to the 360|Flex sessions in the Adobe Media Player, follow Ted Patrick's advice from Deleted link his blog post.

His presentation is also on Slideshare, but it's nowhere near as informative or entertaining.

Chapter 7 of the developer's guide deals exactly with this. I suggest you read it.

Excerpt:

Although raw data objects, such as an Array of strings or objects, are wrapped in collections when you use them as the value of a dataProvider property, using collections explicitly is a better practice. Using collections explicitly ensures data synchronization and provides both simpler and more sophisticated data access and manipulation tools than are available when you are using raw objects directly as data providers. Collections can also provide a consistent interface for accessing and managing data of different types.

See also this about data binding and arrays

that would depend on what you did to the data. did you apply a filter, if so you'll need to refresh the data. did you do a sort, if so you'll need to refresh the data. Is your dataProvider an Array, if so this doesn't do binding, use an ArrayCollection.

Give us an example of what it is that isn't updating and we should be able to give specifc help.