I bought Anime Studio Pro for christmas last year. I've had plenty of 3D animation experience but this was my first attempt to use 2D animation software. I'm really impressed! The programme is very stable and crammed with useful tools and features. I don't know what the other reviewer was on about concerning masking. Masking is feature ridden and works closely with the excellent Anime Studio layers system. Thus masking will seems complex at first; you can arrange masks and layers to do just about anything you would expect a masking system to acheive.
Also rather than being a cheap, cheating way of adding features the ability to add functionality via scripts simply emphasises the professional nature of the software. Remember it is user added components that make Maya the 3D software of choice in many professional environments. In the short time I've been using Anime Studio Pro I have found the user community to be extremely friendly and helpful. There are plenty of interesting and useful scripts available, and plenty of help to use them. Anyway there is plenty that is built into the software to allow you to make great animations, and the ability to add scripted extra tools is just icing on the cake. Also, importantly, the quality of output obtainable from Anime Studio Pro is at a professional level.
The vector based drawing tools work really well, and layered photoshop images can be imported. Again the other reviewer should note that outlines (or curves, or lines if you like) are the basis all vector artwork, and other extremely expensive professional animation programmes use similar vector based methods. The lip syncing features are also excellent and are quick and easy to use. In fact quick and easy sums up this software for me.
Compared to other 2D animation products this is undoubtedly the best by far in it's price range.