1 and 2 from your list are the worst.

Navigation is critical, if a user visits your site and find its complicated or frustrating to navigate your site they will just leave. It's important to consider an easy navigation no one likes to end up with a headache.

do not use to much flash

Assuming I am there already because the subject interests me, nothing makes me leave faster than many ads.

Minimization of web traffic is not so difficult but increasing is very important.

Here are some point to be considered,
They are

1. Relevancy of content.
2. Try to make your content visual ,dont simply put more & more more content on your content.
3 Bad images
4 Broken linage

Long loading time takes the cake for me. I'm always driven away from even my favorite sites when they take forever to load. But I don't mind ads on any webpage, because they're all removed for me because I use firefox with the Ad block Plus Add-on.

It really depends, if your searching for an answer I will sit a wait for a page to load a week if I think the answer is their. I will leave a website if I have to bounce to another site to find what I am looking for. That is just wasting my time.

Thanks for all the replies !

Navigation system do play a major part .

Actually, usually, the thing that makes me want to leave isn't loading or colors or anything like that ... and it may not even be ads ... it could just be that I get annoyed trying to learn what the site is about or, perhaps, simply what to do next. I know I've lost members due to that reason.

__________________
Posts Of The Day - Reward quality while getting more exposure.

spam
lack of members
lack of ACTIVE members
abusive mods or admins
overly harsh rules.

Load time is the main factor. because if load time is very high then visitor have to wait for a long time then he prefer to move to another site.