The HTTP client does not handle GZip compression. I don't know if it can internally when handling the contents but the header sent to the server does not tell the server that it can handle GZip so the server never GZip the content.
This is very key as in a Rich-client / Web Service application, it is very possible to have the scenario of a large data set being sent over the wire. GZip compression speeds up the transfer markedly in some circumstances.
The step I did to try is as follow:
1) Activated GZip compression on Tomcat as "force" to be sure.
2) I monitored the network with Ethereal.
3) Connected to the server through my client program.
4) Looked at the headers sent and received.
I saw in JIRA the following entry, marked as FIXED, http://opensource.atlassian.com/projects/spring/browse/SPR-1255
Though, I'm not tracking at all with the comments there.