Make the "Change by" human-readable. The generic Field - Original Value - New Value is really hard to read. For example on this bug, there was a change by Anton today with three fields updated. Takes me a while to read all that with the table format. It would be so much more readable if it looked like this:

Edited by Anton Mazkovoi [14/Jul/05 05:35 AM]
...Fix Version/s set to 3.3 [11121]
...Assigned to Dylan Etkin [dylan@atlassian.com]
...and Priority changed from Major [3] to Critical [2]

For a resolved bug, something like:

Resolved as By Design by Anton Mazkovoi [14/Jul/05 05:35 AM]
...and Assigned to Dylan Etkin [dylan@atlassian.com]

Something like that. So the first line would be what happened, and lines after that would simply say in English what changed (similar to how the workflow editor prints field change tasks in English). It would be so much easier to read, and then I'd just leave my browser in "All" mode all the time.

This is what MS's Product Studio does, and it's really nice and compact.