Fortunately, and possibly because I natter on constantly to him, Ben's speech seems pretty advanced for his age, or at least nothing to worry about. There are a few words his mispronounces - such as "wadigal" for triangle - which I find endearing.
But a couple of my friends have had concerns about their little ones' language skills. As with any other area of development, there is a wide range of what's considered normal for each age group.