I consider GTD to be an all or nothing system, i.e. either you fully engage in the system or you don't. I have found that using bits and pieces of it doesn't really work. But, I've been reading about Pomodoro lately. Can it be used in bits and pieces? Are there advantages to diving in and fully embracing it? Some of its steps, like the logs and marking interruptions, seem hokey and I'm not certain they seem all that useful.
Yes. You will likely get more out of using in completely. However I can think of two ways where part would be useful:
1) Just using the timer. I do this when I'm working on a project home to remind myself to take regular breaks. I find this makes me focused longer.
2) Just using it for certain activities, but not all day.
It has a minimum which you need to adopt (i.e. the atomic timer), but it's definitely not all or nothing.
I find that logging interruptions and predicting pomodoros do help greatly and work perfectly with the system, but they're optional. In fact, I get more productivity by those, rather than the timer itself, because my work doesn't always go well with the timer.