You are actually encouraged to comment on older posts! You don't realize how much reddit influences you until you are on such a liberating website. It's pretty difficult to seek out some of the older ones to comment on, but insomniasexx came up with a great way to get used to it (the Hubski newsletter). Don't be afraid of creating new tags if you can't find what you are looking for either. People like you here and you won't know if they don't. Ignoring the user is completely up to you.
I earned my first full hubski wheel yesterday and got shocked when it disappeared! I didn't realize how much I was glad to see the damn thing, so I'm back to earning another one for the sole satisfaction of seeing it up there again.