OScommerce is ok but if you want to SEO the store and have many inexpensive custom modules available MIVA Merchant is much better. OScommerce is open source (which is good) but MIVA Merchant is supported by the host.

We used oscommerce,just like zencart,they have many plug-in, i think it is good.

I use zen-cart on all of my sites. I think zen-cart is more secured and powerful than OSC, IMO.

It all depends upon your requirements, OSCommerce is fine for beginners, as you grow online you'll find yourself requiring additional modules, its going to get time consuming and technically buggy to add additional modules yourself. I would start with oscmax or creloaded or zencart.

I prefer magento much more

Try using PrestaShop, a good script for online sales.
You will find good support plus a lot of free plugins on their forum.

Yeah oscommerce is easy to use and required less resource in server than others in my view ....

Easy to change osccomerce template too and its will charge less in maintaince too where oscommerce skin charge is 80$ where others small shopping cart changes start from 100$

Its is my personal view.

Regards