I'm using Selenium on a major project, and from the start refactored out common tasks. I record new tests using the Selenium IDE formerly, now the Sauce Builder plugin, then export to code and replace quite a lot with calls to our own much-simplified API (often cutting out huge sections of test code & replacing with one call).

Updating the tests even when we make significant changes to the website is must easier because of this approach.

One issue we ran into quickly... tests need to verify just one thing as much as possible, not long strings of actions that wander through the whole site. The problem is that there's considerable setup before testing that one thing -- creating users and getting them to the appropriate state, especially (worst of all when test cases require 3+ users to interact).

To address this I've set up some helper requests Selenium can make -- actions that aren't included in our production build -- to create/destroy test users of different types & in different states directly. I'm also thinking of adding a page that'll simply return a full dump of info on a given test user, so we can test that the end result of actions in the UI have resulted in the expected data.

It's all very much work in progress, but I'm convinced that with a little extra elbow grease added as pain points show up, we can keep a full suite of Selenium tests alive and useful.