Since I started using CiviCRM about 5 years ago I've thought one of the biggest problem areas was related to tracking and searching for contributions based on household, which is generally how non-profit contributions should be tracked. It's been the source of many struggles at 2 or 3 orgs I have been associated with during this time.
Soft credits have helped to some degree, but require consistent and mistake-free work. A possibly very useful solution occurred to me last night - what if any time an individual makes a contribution it automatically soft-credited the household they are a member of?
Ideally it could be turned off and on and have the ability to control based on financial type.