I've not taken a child to a speech therapist, sorry, but if it helps to put your mind at ease, DH and I both had to see them as pre-schoolers - I was saying a lot of words back to front, (was also very hairing-impaired), and DH replaced the ends of each word he said with "gah" (how random is that?!?  Ah, kids eh).  My mum would tell you that even with the rocky start that sure as hell didn't stop me from talking her ear off... heck, I can't even type a brief post here!!  So much going on and on and on to be done!  So even though it does seem like he's taking his time with his speech compared to a lot of his peers, remember that those milestones aren't instructions on how toddlers are to develop, they're just very general averages, and doing something earlier or later than the usual is no reflection on his abilities.  That said, I don't think there's any harm in seeing a speech therapist - they're well used to working with preschoolers and the sessions are made 'fun' for the kids.