Do I Really Need a TriBike?

You can do a Search (Upper right hand corner) on BT for Tri bike vs. Road bike. There is a new thread on it about every other day.

Do you NEED a tri bike? Nope. What you NEED is a bike that fits your lifestyle and how you plan to use it.

I have a tri bike and a road bike. I ride my road bike all the time in group rides. I'm more comfortable on it in general and like it more than my tri bike. I have done a HIM and an IM... both on my road bike. Felt more comfortable on hills with my roadie so left the tri bike at home.

For ME a road bike is more useful. Others will say they won't ride anything other than their tri bike.

For everyone it's different.

Either a road bike or a tri bike will suit you well.

If you:
are going to do technical and/or a lot of climbing HIM and IM
are going to ride with people
want to just have a decent bike that is very versital

Get a road bike

if you:
Want to do solo rides or ride only with other triathletes
want the faster bike (but your training counts a WHOLE lot more than the bike)
want to use muscle groups that will help your run

Get a tri bike.

Yeah, there are arguments both ways and people will even argue some of those points but those are the biggest questions asked.

You will get a lot of that time back on a roadbike in your races. Do you NEED a tri bike, No. Get a roadbike first and in a few years decide what you want again.
I have both and split my time between them pretty evenly. Did lots of tris on roadbikes and lots on tri bikes no huge diff unless you are top5 in agegroup then it matters.
John.

Get both! 

Seriously though, they are both tools that have different uses/abilities...

I love my tri bike and I do all my riding solo and it's fast.  However, it is a aggressive, a little cramped/compact (as it should be), twitchy steering, a little harder on the hills/technical stuff.

However, I wanted to expand my riding a bit so I just ordered a road bike.  I wanted something a bit better to climb with, something I can join in on group rides with, something that might be a little more relaxed and stretched out for some epic rides, etc...

I sort of think of my tri bike as a two seater sports car, fast and agile, but maybe not the most comfortable to commute in.  A road bike could be like the luxury sedan that is still uber fast, but maybe a bit more suitable for day to day driving and long road trips.  That's just my take.

BTW, my MTB is like a 4x4 obviously!

Thanks everybody.  I did read a couple of other threads with similar discussion.  I am not going for tops in my age group.  I like to do well but mostly I challenge myself.  I think the long term value is probably in the road bike.
Does the geometry of a tri bike help improve your running muscles or help you conserve your running muscles for the run?  I guess the geometry also makes it easier to get in a cleaner aero position, too.  That doesn't look very comfortable to me.  But I'm guessing it's not much different -- comfortwise -- from leaning out over a road bike.
I guess I need to do a little research as I wait for the end-of-season sales.

If your bike isn't comfortable riding a half or full century, your bike fit is wrong and/or you haven't got enough miles in the seat, no matter which bike you got.