I took a week off at my previous job to trial at Weebly. My previous job had a very strict vacation policy, but I knew the importance of what I was doing.
Weebly has an unlimited vacation policy, so, it worked out pretty well.
You've mentioned this twice. Yet, it means nothing for vast majority of people in the workplace. The majority have to be at work programming instead of interviewing for programming positions. They neither have unlimited vacation time nor a 100% guarantee using a vacation for some interviews will go anywhere. If anything, the OP's post shows quite the opposite for them in common case.
So, how does a trial week work for candidates committed to another job? If anything, it seems to self-select for part-time or remote workers that are already in a position with time on their hands. The best I know don't fit into that category: you'd miss them.
EVERY job switch has inherent risks. It's unreasonable to expect otherwise. No one can help that and OPs situation wasn't crazy. He/She took a risk and it paid off. The downside is just a lost week of PTO? Not too crazy and anyone with a full-time job and some PTO could do this. I'd even get 'really sick' if I had too.
It's true that every job has risks. Where do you see me (or OP) say otherwise? The question is should every candidate give up a whole week of his or her time knowing it will get most people nowhere. That method's benefit is almost entirely rigged for the hiring party with huge potential for waste for other party in any environment with multiple, decent candidates. A few anecdotes that worked out don't change that.
So, the question is: "Should employers put this kind of burden on every candidate or try a method which demonstrates skill with less time?" I push for the latter.
What a disaster though, if you didn't get the job.
1) Lose a week of PTO, and
2) Feel really bad that the people you spent a week with didn't think you were good enough.
Also, from the Weebly end of things, what if you know a couple days in that the candidate isn't going to work out? Cut them off right then or finish out the week?