I love Anki, been using it for the last year. What has been most powerful for me, is that I no longer take standard notes when trying to learn a new topic. Instead, all of my notes are in "question" form, so that I can keep on top of it over time. The spaced repetition keeps my learning efforts efficient and keeps things from leaking out of my wetware memory.

The synchronization feature between devices has also proven to be very useful, as I use my laptop usually to put in new questions, but use the iPhone app to quiz myself whenever I have a few spare minutes during the day (waiting in line, walking to work, etc).

UI is a little wonky at times, but its features and flexibility more than makes up for it for a dedicated student.