Mouseovers are one of those things that seem superficially attractive but require very careful tuning to maintain a balance between annoying and useful. Currently, for thread popups, DPR has all settings hard over at the annoying end of the scale. Here are some suggestions for improvement:
1) Make thread popups a user selectable option.
2) Improve the threshold for when a popup appears. The method is something like "if the mouse is on a sensitive region and is stationary for x milliseconds then popup appears", the key concepts are stationary (just moving over a region does nothing) and the time limit. Ideally the time limit would be user selectable (for threads, I might choose 5 seconds, others might choose 1/10th).
2a) Note the top of page dropdowns appear just a bit too quickly because it ignores the "stationary" requirement.
3) This is what DPR has wrong IMHO, a thread popup (but not the top of page dropdowns) must disappear as soon the mouse moves.
3a) (for experts) hitting, say, ESC dismisses any active popup until conditions change
4) There is plenty of wasted space on the left hand side of the page, why not display thread popups there? That way nothing is obscured (which is 90% of the annoyance value).
The top of page dropdowns are basically OK but appear too quickly, just moving over that bar should not cause the popup to appear., the thread topic menus need tuning.