JSRs over time
In tackling this question, I decided to focus on the simple statistic of how many JSRs were submitted per quarter over time. This does not address JSRs that were never finished, or how long the JSR took to complete, or whether it is still active and in maintenance mode.
The data as to when a JSR was submitted is publicly recorded on the JSR page, for example JSR-311 was submitted for voting on 13th February 2007.
So, without any further ado, here is the main graph of JSRs submitted over time. The red line is the total of all JSRs (Java SE, EE and ME) while the green line is only SE and EE:
Hopefully, the trend is clear - the number of JSRs submitted has been falling over time. To be clear - only 5 JSRs were submitted in the whole of 2008, and only 4 have been submitted so far this year (roughly 1 JSR per quarter).
The question is whether this is a worrying trend, or just normal for a maturing language. I suspect its a combination of factors.
In part, Java is now a platform where most innovation occurs outside the JCP. This is a good thing, and shows a healthy ecosystem that doesn't need the 'blessing' of an official standard to make a technology or product useful. Examples of this are Spring and OSGi - both were widely used without a JSR (although ironically both now have some connection to the JCP).
Another factor is that a lot of the Java EE work, and possibly others, appears to be going on as maintenance revisions to an existing JSR. This doesn't show up on this graph, as the no new JSR is created. This is fine, although it may suggest an unwillingness to go through the process of starting a new JSR.
One more point worth noting is the timeline. JavaOne 2006 was when the Open Sourcing of Java was announced, and Sun developers were taken off active development to begin the very long process of legally reviewing the entire Java codebase. This was then followed by the (mis)adventure of JavaFX, which drew even more developers away from core Java and new developments. There may be some signs of this in the graph, where the steady state of 2004-2006 declines at the end of 2006.
Finally of course, there is no doubt about the absence of Java SE JSRs for Java SE 7 (language changes and API changes). I've written before about the politics behind this.
Certainly I see the JCP as being at a crossroads. The Oracle acquisition is key here. Oracle could choose to reinvigorate the JCP, with industry partners, ideally separating the JCP from Oracle itself, as IBM did with Eclipse. However, given the money Oracle is spending, I suspect that won't happen, despite their previous sentiments.
Unfortunately, continuing the status quo doesn't wash either. At present, the JCP is deadlocked on how to proceed with the Java SE 7 specification. As a result, JDK 7, Project Jigsaw and Project Coin are proceeding outside the JCP. Plus of course, JavaFX isn't related to the JCP at all.
The JCP has considerably fewer JSRs being submitted now than the 2000 to 2003 period. This doesn't quite mean that the JCP is dead or no longer has value, but its another data point as to how Java is maturing and stabilising. Or perhaps less kindly - fossilising.