At work I'm taking over a project and to get my head around the requirements (which were a bit thin) I decided to mock up some of the pages.
In the past I've done mockups in simple HTML, Illustrator, Fireworks, etc. I've grown fond of Balsamiq however. It's a very simple Air application that allows you to quickly get your ideas on the screen. Since I last blogged about it Balsamiq has become a very mature tool - you can export to PNG, PDFs. You can create links between different mockups and then click between them giving you a very realistic idea of how the user interface will work.
What is really neat is that another company has built a companion tool called Napkee that allows you to take your Balsamiq mockups and convert them into HTML or Flex. I tried this on a few of my mockups but was concerned with the heaviness of the HTML markup it produced. If I took some more time to outline my Balsamiq mockups this may make the markup Napkee produces more usable moving forward. I would be interested to hear from anyone who uses this for Flex work. The concept is certainly there and I think with a bit more work the two will become a very powerful combination.
While I spent a few days doing mockups, clicking through them and tweaking links to improve the usability of the application I think the time was well spent. It is much easier to quickly edit a Balsamiq template than hack even the simplest HTML.
Next up - error logging...