An interesting problem occured recently, and I've been thinking of the "best" way (for a given value of "best") to implement this.
In essence, it's one of tracking notes against source code. The example that flagged this was getting a problem fixed in live within SLAs, and how to best achieve this. Without going into all the details, it came down to finding a function that's used in a number of places which may or may not be buggy, yet the problem was being reporting only in a single location.
The fix to meet the SLAs was simply to add a check into the location where the problem was reported, rather than tweaking the common code and having to test everything that touches that function.
The interesting issue is then for upstreaming. The "correct" method would then be to go back and check the original function, validate it's correct for everywhere it's called and then make the change "properly" if its determined the library function is wrong.
The problem is this takes time, so upstreaming may simply take the workaround, etc. However if the problem occurs again (say six months later) in another location calling the same library function, there isn't an easy way to link the two problems together. You can search the bug tracking database, but this isn't guranteed to help - it depends if a note's been added saying something along the lines of "this library function needs more thorough checking, but no time to investigate now".
So the question is this: within a large team of developers (30 plus, split into teams of both support and on-going development), what methods do you use to manage (what are effectively) "sticky notes" against source code, short of adding a comment to the suspicious function's source code saying "this might be a bit dodgy"?
The problem with the commiting a comment is one of process: a change is a change, so committing a zero-change change (i.e., one where just comments are added) is not ideal; developers can make mistakes even adding a comment (hit a stray key or something) so it's always (IMO) better to commit only where actual changes are made.
Now a wiki could be used to track per-file notes, but we've got a minimum of four branches and inexcess of a few hundred files (SQL objects, source code, XML files, etc), so a wiki will get unmangable quite quickly.
This is the sort of thing that it would be nice if SCM's could support - bits of metadata against files that are simply notes, but don't add to the SCM's version history - that can be displayed when doing (say) an svn update, or manually viewed.
There may already be solutions out there -- so how do you manage this type of knowledge sharing?
Well we're now using this method: in each folder checked into SVN, we've created a .url shortcut (this is Windows we're dev'ing on) that links to a page on our development wiki about that folder. Thus we can update the Wiki info freely, and on checkout/update everyone gets a link that will take them to the appropriate Wiki page for that folder/module.
We've not long instigated it so we'll have to see how well it works long term -- but it's better than what we had before (i.e., nothing :-) ).