SpringSource: Grails plugins
More often when I install a plugin, doesn't recognize it. For example using Joda Time, I have a variable LocalDateTime date (i'm importing joda library) and eclipse says unable to resolve class LocalDateTime, though the application works. Or I have installed the grails icepush plugin but after the installation taglib files were missing.
It's a SpringSource problem?
You are not doing anything wrong, chances are the eclipse toolset is still behind the competition. As mentioned by @Burt, you can get the STS from SpringSource directly or you can get IntelliJ IDEA which also has a very good clean interface to Grails applications. The latest 9.0.3 works very well with large, complex Grails applications, and seems to have a very advanced intellisense (autocomplete) capabilities.
You should upgrade to SpringSource Tool Suite (STS) which is Eclipse bundled with a suite of plugins. It has great support for Groovy and Grails. 2.5.0 was recently released and it has a plugin wizard for installing, updating, and uninstalling plugins, although it supports plugins installed from the commandline too. I find I sometimes need to manually refresh it but that's simple - just right-click on the project and select Grails Tools | Refresh Dependencies.
After installing you'll need to add support for Groovy and Grails - that's available from the Dashboard.
Download from http://www.springsource.com/developer/sts