Does anyone know the origin of this conventional wiki feature, that allows one to search for occurrences of the PageTitle by clicking on the PageTitle? Maybe a proto-backlinks function? I personally never use it and would be curious to know if many of you find it useful.

I never use it, and have also questioned its value.

Ya, I agree...I never use it. I saw a mod'ed wikka which had the link changed to a different function that I thought was pretty neat, but cannot remember what (sorry). As a proposal, what about being able to set it in the config file so that the site owner can set it to go to a specific page (like search, advanced search, index, homepage, etc)?? That might be useful....altho' also potentially confusing as different wikka sites would have different functionality on that link.

I think that from the point of view of usability, multiplying the possible functions of this link is inappropriate. People usually click on the page title, or whatever appears in the header, to go back to the homepage. Currently, though,
1) there is no such link back to the homepage, except for a small link in the navigation menu
2) there is a huge link for performing a search for the page tag on the site, whose utility might be challenged and which most people not familiar with wiki conventions would find weird.
The solution that personally I prefer consists in getting rid of this link ( see for example: http://webepistemology.org.)

More generally, I've always found somewhat confusing that wiki pages display
a) a site name (for instance "Wikka")
b) a clickable pagetitle (like "SearchHelp")
c) a main page heading (like "Searching in wikka").
This is IMO what makes most wikis look terribly "wikish" (much as many portal suites look horribly "portalish"), while I think a good wiki engine should be smoohtly "hidden" behind the curtains and give the impression to the user of an ordinary site.

We should consider that Wikka now supports SmartPageTitles: a good page title need not correspond any more to the page tag. With a simple hack the smart title might even appear in the header instead of the clickable pagetag.

Why shouldn't a site name (like a clickable textual link or logo in the header) plus a plain page title (a human-readable page heading, appearing also on the title bar of the browser window) be enough?

Well, I found at least one use for this feature:
on, for example, http://www.worldwidewiki.net/wiki/WikkaWiki you will notice EnglishLanguageWiki at the bottom, which leeds to the folowing page:

"By clicking on the title of this page you will find links to pages describing wikis using the english language. This is possible due to CategoryTag and BackLinks."

Check out the mod I made on [[http://wiki.samuelooi.com my wiki]] - clicking on the link edits the page. Clicking on the WikiTitle, loads the wiki HomePage...

Cheers, Sam

My search does not work. Whenever I search, I get redirected to the homepage. What can be the reason?

It looks like a rewrite_rule problem - make sure the base_url value and rewrite mode in wikka.config.php are correct - see http://wikkawiki.org/ModRewrite.