My biggest gripe with it is that it has too many functions! It has lots of those "people who bought this also bought" and "top ten best sellers" that I so hate in online shops but it doesn't allow something as basic as separate thumbnail and large images of products.
In theory it can all be customised online through an admin panel but then you just end up with a shop that looks like all the other osCommerce sites. I want to strip out all the extraneous stuff and change the look of it.....
.... so I'll be taking you up on the offer of help with PHP before too long I'm sure.