I have been using eCart for about 18 months, (this has just been a hobby for me until recently, but I am now starting to think about doing this commercially.)
I have created 2 ecommerce sites, the first in asp just over a year ago, and the second, my first in php, I have just finished.
The first site sells equestrian equipment, and although not as polished, uses size and colour options in the cart.
The second utilises a lot more hand coding, (voucher codes linked to database, customer can't add more items to basket than are in stock etc.) but you don't really get to appreciate these as a site visitor.
If you are interested, take a look.
**url's removed as now redundant**
I am happy to help or advise