Rob, yes - the error you show is some problem with mvn repository resolution and it seems to be concerning certificate for repository.jboss.org - I know there have been changes to the certificates on jboss.org recently but that is a month or longer ago so weird you should just have that problem now ?
Any chance you have had your eclipse running for weeks without a restart and it might have cached old info ? (reaching for straws here ;)
The reason for eclipse becoming a drone could be caused by m2e or maven core going haywire about the missing certificate but could also be that it triggers some constant updates to the workspace resources and then trigger all eclipse builders making the situation worse since it tries building the world ...
I know it sounds insance, but have you tried restarting eclipse to see the problem continues ?