TL; DR: Most GOMS techniques are hard work and deliver dubious value. However, playing with the simplest variant, KLM GOMS, is a great way to improve your understanding of detailed interaction design. If you want to be a better designer then this kind of thing is worth doing. Thanks for making it easier, Danny. Otherwise, good quality tips (like Luke Wroblewsky's 'UX How-To' videos) will give you most of the answers.
In detail... Well, first up, it's worth saying that GOMS is a family of techniques rather than just one thing.
Most members of that family try to convert human behaviour into something like a programming language. Those techniques have fallen out of favour because they're convoluted, require a great deal of training and effort to use and are incomplete / unrealistic / dated (take your pick) models of behaviour. The evidence that they deliver useful results is rather thin, I'm told.
Danny's focus here is KLM GOMS which is similar to the common practice of figuring out which interaction is most efficient by counting clicks. KLM GOMS goes a bit further by adding in things like 'thinking time'.
I rather like this technique. It has it's pros and cons.
In its favour
- It makes a designer think carefully about what they're asking the user to do. It's surprising how much effort it is to
- It allows designers to analyse the efficiency of alternative prototypes and sketches more accurately than is possible in a think aloud test, more cheaply than is possible by building two designs and running an AB test and more objectively than sitting round a table arguing.
- It highlights some important principles in interaction design - such as the need to keep users in a flow. Conducting a few KLM GOMS analyses is a powerful way to learn what's good practice.
- It's a rigorous analytic technique that's hard to automate. It can be hard work.
- It's not suitable for interactions that last more than a few seconds.
- It assumes the user is familiar with the interface (so it doesn't tell you much about novice users).
- The 'thinking time' approximation is problematic.
I could go on, but that's the gist.
With that in mind, I seldom use KLM on projects. But I do use it to help derive and teach principles and tips for interaction design which are easy to apply day-to-day.
If you've not had a play with KLM, I'd say that it's worth looking at. It'll give you a deeper understanding of what works and it'll help you appreciate (and create) good details in design. When I teach it, I'm always surprised at how much people get from it and how enthusiastic they are about it.
Jeff Sauro has a nice example on his Measuring Usability blog which should get you started. The book The Humane Interface has a very discussion of it.
Anything that makes KLM simpler (like Danny's spreadsheet) is good news for me!
If you just want some tips, check out Luke Wroblewski's videos on YouTube on improving forms and input fields. They're excellent.