I've been using osCommerce for many years building sites both for myself and for my customers. At this juncture I'd like to add that although the core osCommerce code now contains deprecated code it is still solid .. and very well coded .. still well worth a download.
Having said that osCommerce portrays itself as being a solid base from which on line shops can be built, a fully working shop but a template if you like for a "propper" shop, however . . it becomes apparent to most early on that work has to be done on the core before thoughts of adding contributions can even be considered even though it does function "out of the box".
I found myself writing a header/footer mod that removed the need to alter all 28 files in catalog to attain a basic design, also like many others I read the optimisation threads to try and curb the runaway 200+ queries. To cut a long story short(er) I built a "personal version" that was easier to template for customers and more efficient for speed/queries.
The development of osCommerce has slowed to .. well nothing at the time of writing. Deprecated code of the type in existence all over the osCommerce script like predefined long arrays ($HTTP_GET_VARS etc.) and key variables in the global scope is not what the current shop owner is looking for, not even a valid DOCTYPE never mind valid code!, also oscommerce is terribly time consuming to template even for one who is fully up to speed with the code.
If you take a look at the osCommerce contribution offerings (as huge as it is) you'll note a virtually total lack of templates after 5 odd years as a "top download" quite amazing! if you look as a comparison at the simple machines website (SMF - my favoured forum software) you'll see close to a thousand and those are just the free ones! Users want "plug in and go" templates.
The initial concept for the build of obcommerce was to fill these holes but it is also our intention to retain a core solid base code not a feature ridden coding nightmare. The current version of obCommerce will soon be made available for beta testing to select individuals and the main added features currently are: -