Julien has a comparison of open source application servers in which has an interesting quote about Geronimo's startup time :
"The startup is a bit slow: I suspect that the GBeans framework (IoC) flexibility price is some CPU time."
The interesting part to me was Julien making a connection between startup performance and IoC. Trying for myself the Tomcat incarnation of Geronimo 2.0.1 (at 55MB, the download is the same as GlassFish v2 which comes with clustering, WSIT, and OpenESB), I obtained the following start-up time -
On my machine, using Java 6, a Geronimo warm start is 43 seconds (cold start with Java 5 is 60sec). A good chunk of that time is taken by starting the EJB container. GlassFish v2 on the same machine starts in 10 seconds (stopping actually takes almost longer than starting!).
To be fair, startup time was an important effort for GlassFish v2 resulting in not all services being started as part of those 10 seconds. So I also tried Little-G which also starts up in 10 seconds. Such identical figures don't make startup-time an argument in favor of having the stripped-down version.
As a reminder, the demo of the preview of GlassFish v3 this year at JavaOne showed the HK2 kernel and the web container start in about a second. Now GlassFish v3 work is only starting, but I understand the goal is to improve startup time and to contradict Julien's thinking about flexible architectures ;). Modularity shouldn't come at price.