Just for grins I downloaded the 64-bit Windows version of the new Eclipse beta and it ran fine for me. But other than not having to install a 32-bit JVM into 64-bit Windows, I don't see any advantage to using 64-bit Eclipse.
Peter, well I have only one jdk/jre installed and its 64bit for sure.
Be careful of statements like this. Your browser might be using a 32-bit JRE to run applets since, as far as I know, there is not yet a 64-bit Java plugin for running applets. Look carefully in Programs Files (x86) and in the registry.