Lot of conflicting info here.
I post on some forums related to my niche, I don't see how it can hurt as long as you aren't spamming or doing anything dodgy (like the OP
If you bring a strong contribution to the forums instead of just posting 1 line responses to get a backlink you might gain some loyal new readers.
I believe diversity
is the new SEO catchword (although I might be wrong, I'm no SEO guru as my rankings would suggest). Spread your link building across multiple methods and sources rather than just focusing on one thing, at least that's what I would do.
I just started a new gaming blog and have gotten a decent burst of traffic in the last few days just from a couple of forum posts (haven't even really done anything here yet) and a reddit submission. Thinking of diversifying into stuff like submitting gameplay videos, maybe some more blog commenting and perhaps looking for another forum or two related to my niche to join.
Always open to other suggestions too, but will start a new thread shortly for that purpose.