May i suggest 2 possible evolutions to your plugin ?
1) it would be great if we could change a bigger portion of text than just a string (i mean via a textarea and not just a form field). This would allow to place some content anywhere in the posts or pages. We use your plugin on one website where we have to put same small panels of content in different pages (like table of contents if you like). For instance (we know it's not meant for that but it's useful) we put : [Panel-12] in the text in different posts where we need to and replace it with some code : <div class="xxx">Title
<link1><link2><link3></div>. This way when we have to make modifications we just made them one time, not on all posts.
2) it would also be great if we could decide to execute a permanent replacement in all posts (with the risks implied) or just a search and replace. For instance on one site, we put lots of links to a website that changed it's structure. So we had to change all the links to this website to avoid dead links. We used a search and replace, but it slows wordpress unecessary : the plugin needs to search and replace the links each time a page or post is called. We need to apply this change in the posts once and for all. So it would be wonderfull to have the option : permanent replacement or not.
Thanks for this great plugin !