The mailing list for developers is:
NB: Previously, the scala-tools mailing list was used for discussions, and an archive is available.
Bugs can be reported on the Tickets Page. You can report the bug as an 'anonymous' user or you can register and log in. Please include the version of the Scala IDE you're reporting the bug against, and also any other details of your platform and environment which might be relevant. If possible please try and provide a small Scala file or a minimal exported project which illustrates the bug with your report.
Finding the Scala IDE Version
In Eclipse:
The version number is the text which follows "Scala Eclipse Plugin" and should be of the form x.x.x.rxxxxx-bxxxxxxxxxxxxxx. eg. 2.7.1.x15067-b20080519123132.
Exporting a Project
In Eclipse:
Please use your judgment when posting an exported project. If it's more than 10kbytes or so it would be worth seeing if you can minimize the project some more. If you can't then, rather than attaching an outsized zip file to the Ticket report, please ask for advice on how best to send the example to the people who will be looking at the bug.