Far too often I'll get email like this:
Have you started looking at this one yet?
It may surprise you to learn that I do not memorize all my bug numbers. Please include a brief description of the bug in your message so I have a clue what you're talking about. The bug title is a good start.
It's like going to a doctor and asking, "What's your opinion on patient 1732?" You'll probably get a better response if you ask, "What's your opinion on Mr. Jenkins, the one in A113 who hit his head on the sidewalk?"
Addendum (since I know people are going to bring it up): Inside Microsoft, many teams use the defect tracking system to track things other than, well, defects. For those teams, it would more properly be called a "things that will require time" database. Records in the database might be bugs. They might be feature requests. They might be work items. They might be requests for collaboration from customers. I was once on a team that used the defect tracking system to keep track of vacations! Using the defect tracking system to record everything that consumes an employee's time means that you can generate a "How many days of work remain?" report to get a rough idea of how you're doing on your schedule.
Even teams that use the defect tracking system purely for tracking defects will usually have entries for things that aren't defects. For example, a defect report typically goes into the defect tracking system as soon as the report is received, before it is confirmed to be an actual bug.
Some teams maintain two databases, one for "potential bugs" and another for "actual bugs" and transfer records to the second database only after the bug has been confirmed. To me, this just seems like a bunch of work for no real benefit. Well, okay, they get brag about their low bug count since they make it hard to get something into the bug database in the first place. (This strikes me as just playing games with numbers.)
Addendum 2: I've been told that these useless email subjects are exacerbated by our defect tracking system. When you highlight a record and pick Send Mail, it generates a message whose subject line is... just the record number. Worse, the mail window is modal, so you can't go back to the record and copy/paste text out of it. At least that's what I've been told; I never use the Send Mail option, so I don't know what it does.