I took my Step 3 last week too. I looked at this site for advice before my exam so I think I should contribute my experience.
I didn't have much time to prepare since I've been on medicine wards and ICU for the past 4-5 months. I subscribed to USMLE world with the intention of doing all the questions. I ended up doing about 500 questions averaging 55 to 65 percent most of the time with 45 and 80 thrown in there too. I think the variation had a lot to do with a significant number of poorly written questions. Anyway, I was short on time as many of you will be so I had to decide between doing the other 800 questions or studying a book. I decided to devote my entire last 5 days of preparation to first aid for step 3. I think it was the way to go because I got many answers right because first aid said what i needed to know very clearly and i read it right before the test.
I also didn't think the questions were all that bad on the actual exam. I feel pretty good about it. No score yet of course, but I'm confident enough to come on here and recommend first aid. I had heard that it wasn't nearly as good as the step 1 version, but I disagree. I pretty much knew all the H&P yields diagnosis stuff already from my steps 1 and 2, but I got some good review of what tests to order, interpretation, and drug choices. If you are comfortable with the presentation of different diseases and can focus on the tests and Rx, it's really not much material to cover.
Anyway, doing some questions is important for getting in the swing of things and getting your speed down, etc. but it just isn't as high yield as first aid.
For the cases, I did almost all of the cases on USMLE World and went over all of them in first aid a couple of times. They were mostly easy. The presentations really are as obvious as they seem on the practice sources, so it's all about knowing what tests to order and treatments to order a specialist to do.
I studied for about 3 hours 3-4 times a week for two weeks then for about 6 hours a day on the weekend before my exam. It wasn't bad. That's coming from a background of finishing 11 months of a prelim medicine internship, but I was by no means the know it all of the intership. Just an average schmo hating intern year.
I don't know if this is helpful at all so I'll shut the heck up.