I've done NaNoWriMo many times, and it can be incredibly useful if you have a clear idea of what you want to accomplish. There's plenty of moral support and encouragement in the portal, but one thing I've noticed is that it's hard to identify a group who are also writing historical fiction.
So, I've decided to create one—a selfish endeavor! I need to push myself back into actually writing (not just editing) and I have a project I started and that I want to continue. If you're interested in joining me, sign up here! I'll create an email group and keep us all going and motivated with check-ins etc. Oh, and in this group, research counts! If that's what you're doing, make some goals and we'll all support you in it.