This is a very good extension compared to other shopping carts however there is absolutely no excuse for the developers not to create a Joomla 2.5 compatible version. I understand it requires a lot of work and time. The question is how come others are able to do it? Create a commercial version or whatever it needs to support the development. As I'm writing this I'm already switching to different shopping carts because we're upgrading to J2.5 for many clients. This is a sad story. A promising work that just left behind....
Thanks for the review! The 2.5+ compatible version of Tienda is nearly ready for release. You can access the branch on our SVN here: http://projects.dioscouri.com/projects/tienda/repository/show/branches/Tienda-DSCLibrary
We'd love to have you come help us test it out!