I used chiefly Stalla for Level 1 - December '07 and Level 2 - June '08 and passed on first attempt.
Used only Schweser (Notes and Secret Sauce only; no QB, no audio/video); Didn’t even read Ethics & SPC from CFAI text. Still I would suggest to use CFAI texts for Ethics related sessions (session 1 and 2) as I had tough time with the Research Objectivity Standards. I still scored > 70% in Ethics, but I am sure I must be close to 70%. I am not sure if Schweser only is a good strategy for LIII. FYI, http://www.analystforum.com/phorums/read.php?13,813694 of LIII forum indicates this strategy may work.
I’ve used Schweser (study notes only) exclusively for levels I and II. I passed both on my first attempt with >70% on all sections except Ethics, and Economics for level II. My background is engineering. To me, official CFAI readings are a terrible study tool. I tried using them for level I and quickly gave up. With CFAI, I study much slower, yet the knowledge retention rate is dismal. There is just too much fluff. I didn’t even bother to open CFAI books this time around. Some people seem to think that Schweser doesn’t cover 100% of required knowledge base, but not from my expericence. Outside Ethics, there was nothing I saw in Level II test that was not in the Schweser notes. * There are, however, areas where it would be worthwile to go outside of Schseser notes: 1. For Ethics, Schweser coverage is inadequate. Suffer through the CFAI Ethics readings, memorising everything, or resign yourself to doing poorly on the Ethics section. I chose the latter 
2. Schweser practice exams are a very poor approximation of the real thing. They differ in structure and focus, and have higher level of difficulty. I’ll try CFAI practice exams next time. * There was the “cost parity” - “cost proximity” term difference. Also, perhaps the fine details of what goes into current or financial account were emphasized more in CFAI, I have not checked.
I passed (surprisingly) with 80-90% Schweser + all CFAI test
I never used Stalla or Schweser.
Stalla only.
Schweser all the way in L1 and L2.
Both exams Stalla only, although I would recommend complementing Stalla with other materials for L2, as I passed only barely.
Schweser only for both 1 and 2, and that’s already too much to read…