First came Joomla 1.0, then came Joomla 1.5. Now there is Joomla 1.6, and there is an early BETA version of Joomla v1.7 available as we speak. That said, the big question on everyone's mind is:
1. When do I upgrade?
2. Do I upgrade?
3. When does the madness stop?
Well, the answers to these questions are like everything technical, "It all depends!" Having been in the software engineering business for longer than I care to remember, I have some good old, tried and true advise for those of you wrestling with this decision. As I always told my programming staff, "If it ain't broke, don't fix it." The same holds true in this case. Software engineers like all folks holding an active membership card in "Geeks R Us", and proud of it, are by nature leading edge sorts of folks, or should I say bleeding edge sorts of folks. They want to have the biggest, best, fastest, and newest technology in their toolkit. This is NOT intrinsically bad, but what it really says is techies can sometimes start chasing the golden ring without considering that sometimes, just sometimes, doing nothing and taking a wait an see approach is the best.
Unless you have some over-riding requirement that causes you to move to the newer releases of Joomla, I would highly recommend stay where you are. The compatibility of many of the applications needed for high-end e-commerce sites is just not there yet. Why bet the farm on related applications that are in the midst of BETA testing? I have 1.6 on one my development servers now, and will obviously install a "lookie see" version of 1.7 sometime later in the year as grows nearer to STABLE, but in all liklihood, C2C's bread and butter platform will remain 1.5 until such time as I am either driven from it by actual need, or all the e-commerce components necessary for our sites catch up, and prove they are ready, willing, and able to run day in and day out in the production world. I have yet to see that.