such a thing as too many characters?

This is a biggy. I got into a debate with some of my writting friends and all of us had something different to say. One said that having too many characters can confuse the writer or worse those he is writting too. Another talked about how having a lot of characters can make a book. (yet very rare too do so) he called it "good writting". in all honesty though, I believe it all depends on what the writer calls for. If he/she needs fourty characters ( even though that is excessive) it is perfectly fine. On the other hand if she/he call for only two characters then that is also perfectly acceptable.

Now I am really curious to see how all of you think!

It is possible to confuse the reader if you introduce too many characters at once and switch between them so often there's no time for the reader to really know them in-depth.

If you introduce small clumps of characters at a time that are very well characterized and cannot be mistaken for other people, then it becomes a lot easier for readers to keep track of them all.

Yes, but only when it gets to the extent where all you have is a large group of characters with little to no characterisation. I'd say you can have as many characters as the plot demands as long as the characters you have remain distinct.
Personally I think if you are considering adding a new character to an already respectably sized cast then check before hand if the new role could not just be filled by an already existing character.

If the story warrants lots of characters, you can have as many as you like. But keep in mind that each book should have some kind of limit. You should always have a new character established propperly before introducing another one, that way the reader can easily tell them apart because they have some sort of attachment to the established one, however small it may be.

Depends on the size and scope of the story. How many characters are there in Harry Potter? More than forty, I can tell you that. A lot of characters can serve for world-building. Distinction is key, you don't necessarily have to flesh-out every single character - in fact that is not advisable, especially with a large-cast, because then you run into the problem of confusion on who the protagonist is. Who should the reader follow?

They should be distinctive though. And they should be believable. Just be careful not to end up with too many talking heads, like the others have forewarned.

Know the difference between the amount of development a main character needs, the supporting cast, and then the stereotypical cut-outs that are just...stereotypical cut-outs. There's nothing wrong with them. They might move the story along in some way and are important in establishing scene and the world. I'm talking about the strict librarians with the oogle-eyes, the funny mailman who sings show tunes each morning, the kids next door who run around pretending to be secret spies. They are characters too, and even without your needing to flesh them out, they still add color to the story.

Yes, there can be such a thing as too many characters. There's too many when the reader can't tell them apart and starts to get confused, when they distract from the story, etc.

However... with delicate and conscious handling, with the abandonment of self-indulgence... no, not too many characters. It's whatever the story calls for. It just takes a certain writing maturity level to recognize what that is.