The more I think about this, the more I believe we shouldn't steer them here.
When we were in beta it made sense because most people didn't know about Salesforce SE, so there was an education process required, and there wasn't as much content to find via a web search.
You've got to ask yourself why they're posting on SO rather than here.
To me, it's got to be because they're not trying to find an answer before posting their question. This is exactly what we don't want. Steering them here will create more duplicate and/or low quality questions, requiring moderation and making it hard to find authoritive answers.
They will find Salesforce SE if they actually search, because whatever question they have will have been asked in some form before. It's usually just variations that people get stuck on these days. Even if it's not a variation, there is so much Salesforce specific content on here that any web search for Salesforce questions nearly always has Salesforce SE as a search result.
If we were to steer them here, I believe it would be counter productive to just send them to the Salesforce SE home page. It would only work if we sent them to the relevant answer to their question, which is a lot more work than just a quick comment on their question pointing them to Salesforce SE.
