Yes, that practice is as annoying as hell.

There is nothing technically wrong with the practice, but it is not ideal. It makes the sentence clunky, and thus makes the author sound less professional.

The second 'as' in the sentence you quote has a very different meaning from the first, and it is synonymous with 'because'. If you offer your friend some suggestions like this, this particular criticism won't be too harsh.

Then again, if he wants to use 'as' so much that he's going to argue with you, it's his funeral!

As far as I know, you cannot use "as" twice in any given sentence, as well as many other words you should not repeat.

Edit:

Darn! I thought I was going to get in first that time!

As far as "As you can see, its been as yesterday when it was last seen," even if you put "it's" in place or the improper "its" I still see not much understandable or grammatically correct with that sentence. Please, correct me if I am wrong.

Regarding the next one, perhaps I am being too critical, but anyone using a singular and a plural in the same sentence and/or not capitalizing words correctly, I would have a hard time taking them seriously as far as any kind of grammar critic or source of information.

there are no grammatical rule?

There is no grammatical rule, or there are no grammatical rules.

What I would suggest is you both read it out loud to the other (no, not the whole book!) and see if he notices it sounds a bit odd. Then perhaps you can suggest something such as "since," or "because." Methinks he will take well to your hinting in such a way. If nothing else, you can use me as a reference/expert and tell him you read somewhere that over-using the same word can be very distracting and that someone used the word "as" five times in one sentence as an example. (Look at my first sentence.) That should take the heat off of you, or as they say…. Never mind.

You know as well as anyone.

"This is as good as it gets"

As you can see, its been as yesterday when it was last seen.

If you couldn't, you'd be barred from using similes, which might cause you to get as drunk as a skunk.
The frequent use of "as" is merely a symptom of the lack of mental agility – the possession of which is necessary to write anything worth reading.

there are no grammatical rule about using "as" more than once. if it were a college paper/theme i would suggesting using another word. if you like, you could suggest that to your friend to see what she says.

hope this helps!