Jquery plugins are a joy to use, and they are surprisingly easy to write. Everyone that writes lots of Jquery code should seek to take potentially-resuable functionalities of code and put them into a nice, compact plugin. In the app I’ve been working on, we have a lot of user-generated content that we don’t limit the length on, so it can grow very large. To combat this, there is the UI pattern on the site that there is a “read more” link available to show the remaining text for the long-winded texts, while just showing a snippet otherwise. This exists everywhere, for lots of different content; hence, the “readmore” plugin was born.
Jquery gives a great, easy-to-use mechanism for extending its API and creating your own plugins. For stuff that looks like it could be useful generally, you should really try to put it into a nice little plugin package. For submit buttons, there is a general thought that they shouldn’t be clicked twice (especially for functions such as financial transactions), so I created a plugin that fits an app that I have been working on recently, where there are many, many submit buttons, saving very granual pieces of content through ajax requests.