A bubble chart without nothing inside is not that helpful, if you can set an icon or image inside the bubble itself can give quickly a hint of what it is. Also it would be nice, if the same bubble value changes position, to have an animation where it grows or shrinks while moving to the next position, instead of completely redrawing the bubble.

I suggest to add some simple arithmetic for the stack values and display them as label to explain the chart in a profession way. Such as showing the total time of all usage for the meeting room. So use sum({0}, {1}) and display it on top of the bar chart.

Add ability to add an additional title (sub-title) below the chart title and style differently that title

We currently use ObjectPlanets EasyCharts and they allow you to define a drill-down URL that can be associated with each line or bar. This allows us to have a bar chart on a page with a data grid. When the user clicks a bar, a URL is posted to the server that populates the data grid with more detail on the selected chart item.

It would be nice if the charts supported more marker types.  Currently only circles, triangles and squares are supported.  This poses a problem when you have more than 3 series and want to show distinct markers for each series.  I suggest adding support for a cross and star.  It would also be nice to support custom marker images.

Your silverlight Timebar is Briliant.

I suggest you implement something like that(maybe a litle less complex) in KendoUI.