Initially, we discovered that gadgets could be displayed conditionally, based upon the URL being displayed. This is a fairly simple task, when you get used to it - but it requires editing the template HTML - and can look a bit scary, to those inexperienced in template editing.
Recently, we realised that some gadgets can be embedded in a page or post, by editing in HTML mode - and accomplish the same. I demonstrated my custom "Contact Me" gadget, using that ability.
Both the technique of embedding a gadget in a page or post - and of conditionally displaying a gadget - have their advantages, and their disadvantages.
Embed A Gadget In A Page Or Post
My custom "Contact Me" gadget, which is provided by Google Docs as an IFrame embedded page, is published in my static page "Contact Me, Improved".
<iframe src="https://docs.google.com/forms/d/1JvoY2yf5aTChnvXlCgGsUerSCtI7RHpRdkq5SPBPm90/viewform?embedded=true" width="700" height="800" frameborder="0" marginheight="0" marginwidth="0">Loading...</iframe>That's the code for my gadget - you can make your own, in 10 - 15 minutes. You can use this technique with any Google Docs based file.
My expanded Followers gadget is part of my static page, "Followers". The code for that page was provided by Google Friend Connect, and is no longer available. You may now install the "Followers" / "Google Friend Connect" gadget, using "Add a Gadget".
Display A Gadget, Conditionally
Any BlogList or LinkList gadget can be found as rendered HTML, and the code can be extracted - again, from a blog source listing - but both bloglists and linklists are dynamic - and frequently long. If you extract the rendered source, you get a static copy - - which is fine, if you never plan to change your list.
The blog has half a dozen lists, of various types - and I like to add or remove list elements, whenever necessary. I enjoy the Quick Edit feature of the "Peer Resources" bloglist, for instance - and have no intention of publishing that bloglist as a static HTML based linklist. If I was to display "Peer Resources" on a specific static page, I would use the earlier technique of editing the template XML code, and adding a conditional.
It seems as if it should be possible to add XML code, directly, into a page or post. If I discover the appropriate technique for doing that, I will surely update this post.
Know The Alternatives
Just know the alternatives, and choose wisely.