There definitely can be some negative SEO effects of fitting all your content on one page. If you want your page to rank well in Google, the keyword density should be 3-5%, and the title tag keyword density should be as high as possible for the specific term you want to page to rank for.
If all of the content is squeezed into one page, like the example, the page won't rank well for anything (baring off page optimization).
Absolutely. Furthermore, you're going to give yourself a huge bounce-rate if - like the dentist example - you have a single page with no external links.
Google keeps track of how many times users click 'back' from a search result to a search page. Needless to say it's going lower the subsequent rankings that the dentist page receives.
Decreasing the number of pages through clever AJAX use can improve user experience. But it still makes sense to have different chunks of content on different pages, linked together. The SEO implications are a reflection of this.
SEO should never be the reason to ruin a site's navigation. No dentist can bank on being the #1 search for "Dentist" on Google. The dentist's website optimization should concentrate on having accurate information in local directories (online and printed phone books, Citysearch, Yelp, etc.) and encouraging satisfied patients to provide positive online and in-person reviews/referrals. Google Adwords and Yahoo's equivalent would be good investments too, using "<City Name> dentist" as keywords.
One of the commenters made a good point that he had to navigate too much to see the phone number. IMO, the phone number, address, and a link to a map should be on the screen at all times (using CSS fixed positioning).
True, don't ruin your site navigation for the sake of SEO. Good thing its very easy to create a very appealing website that also can rank well in Google.
Having accurate information in local directories would be considered "off-site" factors. Off-site factors are very very important, but does not negate the importance of proper on-page SEO.
And yes, for a website like the example, I think the contact info should always be very easy to find near the top of the page.
"There definitely can be some negative SEO effects..."
There definitely CAN BE negative effects, if you do not know what you are doing. You should be properly building the out the page's hierarchy as well as relevant inbound and onsite links (with id anchors at the end) to accompany that hierarchy.(Please note I am not suggesting links like "http://www.site.com/#about-us" can rank in google)
A one pager, in my opinion, can be great for a small business.
You would definitely need to provide the user with conventions they are used to such as (contrary to DECH's blog post) providing pseudo-navigation at the top of each section.
Of course none of this matters if you aren't putting in any effort to convert that user into a possible customer. So a few things to include:
- scrolling contact info
- contact form
In the end the user get's "faster page loads", and therefore more gratification from using the website.
Disclaimer: This was just a stream of thought, I do not encourage or discourage one pagers for any given case.
1. A high keyword density for the phrase you wish to rank for is very important to achieve your desired ranking.
2. The more content you squeeze onto one page, which could be spread across multiple pages, means the keyword density will be lower.
3. The page will not rank as well as it could have. It's basic SEO. Maybe dentistry isn't a very competitive niche and you can get away with a lower keyword density in the body text.
1. I can beat keyword density out with a good title tag, 2 related headers (h1 & h2) & some inbound links.
2. True, but see my first point.
3. True, BUT only in a competitive market. In my original comment I said "...can be great for a small business.", I probably should have used the words "local small business".
Because ranking for something like... "Miami Electricians" or "New York City Dog Sitters" would be easy and would be most effective (in my opinion) with a one page site.
A good title tag needs to focus on one or two key phrases. If the whole site is on one page, you can't make a good title tag to cover everything. Better to have a different page for each topic and optimize title, body text, and thinks for the topic the page covers. If all inbound links are equal, the optimized page will always beat the all-in-one page.
If all of the content is squeezed into one page, like the example, the page won't rank well for anything (baring off page optimization).