I haven't been paying any attention to the warnings about extras-devel and extras-testing for months, and haven't suffered any serious consequences. I have always found the warnings hysterical.

But let me add a few cautions:

1. I don't install games. If games are secretly destroying people's systems, I wouldn't know it.

2. I carefully check to make sure I have some rootfs space left, and it something seemed to take up a lot of rootfs space, I would probably delete it.

3. My impression is that fewer apps have optification problems than they used to, so dangers are a lot less these days.

4. I am not afraid to flash my N900 when I feel nervous or think it is acting funny. I am a fan of doing eMMC flashing, and think that practically everyone should flash their eMMC at least once.

With the attitude I summarized above, I haven't had any problems for ages; of course, that doesn't mean I won't have big problems tomorrow.