We have a pretty popular forum and are noticing several sites popping up for the same niche that use our almost exact forum structure and even notices. Is this something worth pursuing legally? A recent one is very blatantly obvious and appears to have hired content writers to plagiarize our content onto their copied site.
You can't copyright design or notices, in this context that you're talking about. If the content is copyright, you can action that via DMCA to the host -- providing the host is in a country that DMCA applies.