I can only say that I've seen sites with lots of orphan pages and the rest of the site still does very well in the SERPs. If Google is still crawling those orphans and they do no good any longer, it is better to remove them in my opinion.

This type of thing happens frequently. It can even be intentional such as creating pages targeted at logged in users, or creating landing pages for banner advertising and SEM. I've never suspected them of causing penalties. The only problems I've seen are:
1) sometimes these pages garner an external link and the pagerank from it is not used well.
2) Sometimes googlebot can get into one and from there crawl a bunch of them and you use up some of your crawling quota. Tempting to put them in robots.txt then, but then you lose all external link pagerank.

If they are indeed old or duplicate pages, it is better to retire them and redirect them each to something else appropriate.

Thank you.

My concern was that i found a definition for spam somewhere and it sais:

Doorway pages - Multiple web pages on the same URL that link to your website but have no links from your website.

But Google webmaster guidelines provide better explanation:

Doorway pages
Doorway pages are typically large sets of poor-quality pages where each page is optimized for a specific keyword or phrase. In many cases, doorway pages are written to rank for a particular phrase and then funnel users to a single destination.

So I guess there's no problem there. Anyone thinks otherwise?

In my opinion, if you are not using those pages, keep the house clean and delete them (return 404).

Looking at the second definition given by seopeople, is it not possible that these orphan pages could be seen as doorway pages?

I have been in the situation of having a large number of orphan pages. They would have had links to them if the appropriate user content had existed - each gave unique info so did not want to remove them. They would have had a link to them at some time but only a small proportion are linked to now.

I don't know if they caused me any harm but am in the process of making sure they are all linked to by a permenant link

We typically noindex orphans. Same goes for landing pages. Those pages are not for indexing and are typically used for campaign promotions. The content resides on the main site in another form and/or fashion. I use noindex judiciously. In fact, our template pages contain noindex, nofollow and there are instructions to remove it prior to publishing, I don't take any chances with documents getting into the index that don't belong there. Better to be proactive than reactive.

Well, our situation is a bit more complicated. These are pages that contain recipes. The site template, because of technical and law issues, contain place for links to only 5 recipes. It is illegal for our client to add more links to recipes. However, the recipes are quality ones and they rank quite well in the search engine.

Noindexing them makes no sense... Again - do you think that in this situation it could to any harm to just leave these pages as they are?

I'd leave them.

Doorway pages - Multiple web pages on the same URL that link to your website but have no links from your website.

AFAIK this applies to example.com linking to example2.com, not pages contained on example.com linking to example.com.

If you wanted to you could probably fairly easily create an index page for the pages which links to them, or even just include links to them on the sitemap. Then they would have links to them, which should mean the quote does not apply. (If you can, of course.)

And (Emphasis Mine)

Doorway pages are typically large sets of poor-quality pages where each page is optimized for a specific keyword or phrase. In many cases, doorway pages are written to rank for a particular phrase and then funnel users to a single destination.

Wouldn't worry about it from the preceding if they are truly useful and informative...

However, the recipes are quality ones and they rank quite well in the search engine.

IMO 'If it's not broke, don't go fixin it.', is a good rule to follow.
It doesn't sound like your site's broken to me...

Why on earth would you noindex them and throw away the traffic?
I'd definitely leave them.

Sorry for the double post, and this is more 'rhetorical' and for readers than directed at seopeople but I really don't understand this, so I want to reiterate for future reads and leave them with a bit of thought:

However, the recipes are quality ones and they rank quite well in the search engine.

Why on Earth do people even consider fixing sites that aren't broken?
I don't get it ... I don't get it ... I don't get it

Don't take it personally seopeople, people do this all the time and IMO their inability to sit still and leave what works alone costs them in the long-run, so I want to try and at least give readers pause before they go changing things.

I think the fact that Google (and other search engines) provide the ability to upload your URLs in the form of a sitemap (see sitemaps.org) should be a great indication that having unlinked pages is just fine. One reason sitemaps were created was to allow search engines to get beyond the search box of a website because a spider cannot randomly enter data into a form field and push the submit button to see what happens. That would clog databases all over the planet. Let's say, for example, that you have a database of 1 million recipes but only 1,000 of them are actually linked to from various parts of your site. Google wants to know about these 999,000 orphaned pages that are currently contained in an inaccessible silo on your site because they might contain valuable content.

Sounds good people, thank you for your kind helpful insights.