Hello,
Just a word to say i find it's a pity that there is no more index in AM5's books… Why not create a downloadable index (format exel or OOO for ex) of all books which would enable us to manage a little more easily. The books are very rich and contain a lot of new rules each time, and for not really good english-speakers like me, it is sometimes a little difficult…
Cordially
The rules are usually organized so that the Table of Contents can point you in generally the right direction, but I know how you feel. If you're trying to find something in particular, I'd suggest you post your question here, and I imagine the combined Might of the Atlas Games Forum will be all too happy to tell you where to look. 
Hmmm... What Realm does the Forum belong to?
Maybe it depends on the poster? I'm certainly not Infernal, no sir. I'm probably, uh, Magic. Yeah, Magic. Maybe even Divine. Not Infernal, though. Certainly not Infernal.
I suggest that we have [color=red]ABE do the indexing. 
The Fourth edition books are already indexed...
The index in AM4 : that was really, really useful...
You know, each time a new book is printed, there's a lot of new things...New virtues, new flaws, new abilities, new rules...
That's great, but when you want to find something, you say : "hum, well, i know, i've seen this somewhere...In covenant ? (30 mn later...)...oh no, that's not in..., in HoH:TL i'm sure..., It's a small chapter, i'm sure i've red this..."
And because you red this, you say to your player : "hey, you know, you can even do this !!!...Hu, where's the rule...Ok, i'll find it and i tell you more..."
You're right Erik : the table of contents of the AM5 books are well done and precise...But sometimes, it's not enough to find what you're looking for, specially for me and my poor memory 
(major flaw!!!).
About your proposition of posting on the forum to find what i'm looking for, don't worry : i annoy the ars magica french list whith such questions...