I think tags are most useful when you see them in a "tag cloud." Meaning, the tags you use most often (baby's firsts, food, sleeping stories, whatever!) will be bigger and bolder than the others, so people can look at it at a glance and see that you really like to talk about your daughter's bedtime habits (or whatever the case may be).
Twitter is interesting. You can add your Twitter feed to your blog page (go under "Settings" in Twitter and it will show you how). One way it can enhance your blog is if you tweet about a new blog post, a funny thing that just happened to you, a product you might review soon, etc. It's just another way to let people know that there is a "real person" behind the words on a screen. One caveat though: You gotta update frequently (at least a few times a week) or not at all. Twitter doesn't really work on a "sometimes" basis.