Of course, everybody hates micro-benchmarks. They're easy to quote, but rarely very accurate, and almost impossible to make meaningful. The best advice is try Metawidget with your application, in your environment, to see if it performs acceptably.
That said, and with huge pinches of salt, I thought I'd give it a go. Metawidget already ships with 3 examples of 'retrofitted' applications - that is, existing applications that have been upgraded to use Metawidget. These make for great 'before and after' tests of two versions of the same application where Metawidget is the only variable.
I took the existing JBoss Seam Hotel Booking sample, the JBoss Seam DVD Store sample, and the JBoss Seam Groovy Booking sample, and wrote a Webtest to cycle over them 100 times. I then wrote a similar Webtest (some of the ids are slightly different) to cycle over the Metawidget version. These webtests are under /test/src/web/examples/faces.
- took my PC (Intel Core 2 Duo 8400, 4GB RAM, Windows XP SP3)
- built the samples from JBoss Seam 2.2.0.GA
- deployed them on a fresh copy of JBoss 5.1.0.GA and Java 6 update 17
- set all logging to WARN (I have found logging skews the benchmarks)
- ran the Webtests
|Seam Booking Test|
|Seam DVD Store Test|
|Seam Groovy Booking Test|
Finally I did a quick graph of the results (using GraphJam):
As you can see, the results are all over the place. The Hotel Booking and Groovy Booking samples actually run faster with Metawidget (14% faster and 7% faster, respectively), and the DVD Store sample runs slower (7% slower). The latter result is expected, the former is a surprise. I tried it on another PC just to confirm, and I'd encourage you to try it yourself.
What does this mean? As I said at the start - not very much. Does it mean your application will run faster with Metawidget? No. As they say your mileage may vary. Does it mean Metawidget probably won't have an appreciable impact on the performance of your User Interface and so you should take a look at it? Definitely :)