I also use yootheme templates, the main problem with them is that at the start it´s a bit difficult to understand how it works, and you have to do a lot off css to get the templates done and some php, not too much, but they are really nice.
Other templates like gavick ones or joomlar has virtuemart css done so you can copy from this css and change the classes to work with hikashop, even you can use some nice effects they have.
Both works well, but both needs a long time working on them.
Hope that helps you