Here are three features that your website should not include unless your goal is to drive away visitors.

1. Massive navigation menus at the top of the page that frequently block half the content

If you believe it is necessary to hide your content behind a massive navigation menu, then your content should not be on your website… FULL STOP

2. Flash

If a flash intro exists, I will be looking for the quickest and easiest way to avoid / close the intro and I might even leave the site all together

quote from macromedia:

I contacted Macromedia – the makers of Flash – to see if they
had any formal best practices or advice on Flash intros. Suzy
Ramirez in the PR department sent me a link to a white paper
called, “Flash: a New Hope for Web Applications” (link below.)

Despite the promo-sounding name, it’s actually a fabulous paper
with lots of useful screenshots and examples of how you can use
Flash to make people love your site and your brand. I heartily
recommend you download it.

But, it didn’t have a specific rule about intros – so I called up
the co-author of the paper, Jared Spool of User Interface
Engineering, to ask, “Flash intros – good or bad?”

Jared said, “When we have clients who are thinking about Flash
splash pages, we tell them to go to their local supermarket and
bring a mime with them. Have the mime stand in front of the
supermarket, and, as each customer tries to enter, do a little
show that lasts two minutes, welcoming them to the supermarket
and trying to explain the bread is on aisle six and milk is on
sale today.

“Then stand back and count how many people watch the mime, how
many people get past the mime as quickly as possible, and how
many people punch the mime out.

“That should give you a good idea as to how well their splash
page will be received. That’s the crux of it.”

http://www.marketingsherpa.com/sample.cfm?contentID=2529#

Flash used in essential website components such as navigation menus or used in 100% of the website – this effectively means the website becomes unuseable for some users. Obviously home users can choose to install the necessary plugins if they really want to view the Flash website, but other users might not have that choice. Some users might be within a restricted environment such as an office network where only administrators have permission to install plugins.

3. Sound / Music that plays automatically

Possibly the most annoying feature on a website – the first thing I do when sound plays is either look for a button provided on the website / mute the speakers or as previously mentioned, leave the site.

Thanks for reading.