What kind of event would need to happen to trigger a thumbs down in the WebGUI/send a notification. Just curious as I'm wondering how much I need to monitor these manually vs. trusting the software to alert me to potential problems.

Settings - Notification Settings. Toggle from Basic to Advanced View in upper right. You can customize this somewhat.

I'm not sure what the current logic is for the thumbs down, haven't looked it up yet.  In the past, it seemed like it was triggered by non-zero values of selected SMART attributes, which is better than nothing, but often very misleading, not acceptable yet.  It's early, and I'm hoping for improvement.  Having any SMART checks at all is great, but is still very new.  The SMART notifications have recently been improved, to raise notifications on changes to selected SMART attributes, not just whether they are non-zero.  I want to thank Tom or bonienl for that, don't know which is responsible.  But there's still room for improvement.  The current method WILL report on increases in bad sectors and reallocated sectors (and CRC errors indicating bad SATA cables).  But the current methods do not detect any SMART failures, and that's important.  And they warn on things that aren't that important, and will confuse users.  I've put in a feature request for a change in the SMART analysis that should improve that, plus catch the SMART failures.  Edit:  Wow, that was way too wordy!  Sorry!

Thanks for the info RobJ! I assume it was going to be a bit "odd" yet as it was new, and as there is an issue in either the 6.1 or 6.2 pool to further address this. Are there any good methods for tracking disk health from an external piece of software? I've looked around and haven't found anything overtly useful in the unRaid space yet. I'm thinking something like StableBit drive scanner or something.