As you all already know, a very long and difficult process. For me it's 3 rounds including writing test, coding test, GIA, following by next 7 rounds of interviews. Come with a huge risk that failing any round means the failure of your whole application.
However I would say it's a positive expericence. I know there're complaints about the writing and GIA tests. But after doing some research, indeed they have good reasoning behind, and at least for me it's totally acceptable (there're several posts from Canonical explaining about this). For the interviews, all interviewers I met were truly nice, tolerant, and willing to discuss and explain if you didn't know or got wrong in some topics. And they're all relevant to the role I applied, 4 of them turn out to be my current team members and direct manager/director (and they're all exceptional, which put on me some stresses trying to catch up :))
So my suggestion is, first getting to know about the process and understanding the cost, so you won't get so frustrated. If you need to land a job quickly, dont have much time or cant be so patient, then Canonical's hiring process isn't a match. If you think it's worthy to spend 2-3 months and you agree with the company's philosophy behind, then go ahead. For me, it's also because I've been a big Ubuntu fan for years. But even atm recalling it I still have to admit that applying for Canonical is a true gamble.