SJS Web Server 7.0 Update 1 is out - Focus on Java

If we have GlassFish... why do we need SJS Web Server?

Starting with GlassFish v2, only if you need to load-balance incoming HTTP requests. Otherwise, GlassFish has a very fast embedded HTTPd listener (Grizlly).

Web Server and GlassFish are complimentary servers. They are not replacements for each other. One is extremely well suited for traditional Web server use and the other for the full Java EE server use.
\* If you plan to deploy WARs and EARs - the choice is pretty clear, it's Glassfish. As a servlet container, Web Server is good for developing (see NetBeans support referred to above) and deploying WAR files only.
\* With Web Server's ability to support Java and native non-Java technologies alike, it's a superior platform deploying heterogeneous dynamic content types - Java/JSPs or PHPs, JRuby or Ruby On Rails etc. In addition, as a general purpose Web Server like Apache, Web Server supports SSL acceleration, powerful URL rewriting useful for mass hosting , reverse proxy for load balancing against any HTTP compliant origin servers, and FastCGI for scalable yet safe support for third-party dynamic engines (e.g. PHP, Python, Perl, etc) enables a number of flexible yet manageable deployment options.
If you are deploying to web tier, Web Server is a great choice. If you need a more comprehensive Java EE environment for your deployment then GlassFish is perfect. And as Alexis points out, you can use the servers in tandem with each other (Web Server as the HTTP and SSL termination point, handling access control and static content, load balancing, etc and using GlassFish/App Server as the fully Java EE compliant dynamic engine for the business logic aspects of your application).
Both servers are great solutions, and together they're even better.

Yes, i know it, but it look like gassfish v3 will be very modular, and i could use glassfish only as a servlet engine disabling other options. This will scale glassfish adoption, and if grizzly is as good as it look like, i think that glassfish should have more HTTP options that SWS have ( url rewriting, better virtual hosting, etc)

Just to follow up on this. Joe's comments are spot on. Glassfish and the Web Server are designed to work together and each has their place in the Application Platform depending on your requirements.

Enrique, could you elaborate on the virtual hosting features available in SJSWS that are missing in GlassFish? If possible, we'd like to add them to GlassFish. Thanks!