I found that Wikipedia has a beta facility for viewing monthly page views... so I decided to make a chart to show the level of interest in Scala, Groovy and Java. I charted every month in 2011 and every 3 months before this back to January 2008.
I included the pages for "Computer Programming" and "Earth" as proxies for general Wikipedia use.
Note log scale for upper chart.
The proxies for Earth and Computer Programming pages show that overall Wikipedia usage has not changed much over the 3.5 year time period.
Interest in Java has not waned, and page views have been steadily increasing.
Interest in Scala has quadrupled since mid 2008 and appears to be doubling approimately every 18 months. The surge in April 2009 was due to the announcement that Twitter was moving from Ruby to Scala, and there appears to be a resurgence of interest since January this year.
Interest in Groovy is increasing, albeit at a slower rate. However unlike Scala, it is failing to take market share from Java.
I don't think of Scala or Groovy as an "or" option to Java. I might make an app that uses all three languages. As in Scala and Groovy work hand in hand with other Java classes.
Just 2 cents I had to add.
+1 from my side as well. I have see people make of STM from Clojure in Java, then JsonSlurper from Groovy in Java, Actor based concurrency model in Java and so on. All they require is one jar for each language in the classpath!