Here's my idea:

Many blogs / websites (especially commercial oriented) have standardized data such as phone numbers, addresses, names, company names, zip codes, website URL's, twitter addresses, email addresses, and on and on.... that need to be populated through out the theme / content.

The issue is that much of this data needs be populated in the footer, footer, or other places that necessitate editing code (many are unable to edit code). Sometimes websites that are built for businesses contain the same boilerplate content in the legal, privacy, about, and related pages. Many times these pages include many occurences of words that need to be replaced with relevant data; example: "Company Name" can be reached at "Phone Number" in cases of abuse. Alternatively, you can reach "Company Name" via twitter at "twitter account".

There can be pages and pages of this content that needs to be replaced each time this boilerplate content is given to a new client. Also, if the client ever wants to change the "Company Name", "Phone Number", "Address" or related around the site, they must hunt through content on many pages and code if they want to change occurrences of this data.

I think a great plugin would contain an options page that would enable users to define fields and corresponding tags that will populate the related data through the theme or in posts with boilerplate content.

Example: user can create field for "Phone Number" in options page and define tag for it such as >?php plugin(phone); ? <. Anywhere the tag is placed in the code or in posts (will need non php tag for posts) will populate the corresponding data as defined in options page. If the website owner wants to change the phone number and it occurs through the content and in footer / footer / sidebar / etc. 20 times, instead of hunting down these occurrences one by one the end user can simply change the "Phone Number" field in the backend options page and it will automatically change sitewide....

This could be useful for: 1) developers that use template content as described above 2) developers that want to simplify content customization for the end user 3) developers that want to create themes that are easily customized 4) end users that want to create content with elements that are easily changed across pages / posts 5) affiliates or related that want to set up tags to populate a URL across many pages / posts that want to be able to change affiliate links in the future without necessitating rummaging through months and years of content....