> How long did it take you from day one of learning about Magento to being able to get a cart up and running?
6-8 month of learning in total
> What types of skills did you start with and feel that you needed to do this?
CSS, XHTML, XML, PHP, OOP skills, + Photoshop =)
> How easy was it to get help and how often did you need to get help?
you can get help in magento wiki and community forum
> What are the benefits and limitations of Magento for those who may have used other shopping carts, especially Avactis.
Magento is slow sometimes, it uses heavy frameworks e.g. zend framework
Besides the design integration is not so easy task, like in Avactis shopping cart.
I think that the Avactis is the best choice for designers, and Magento is great with commercial templates.