Lot's of people, like us, need issue locking, even before Service Desk was created. And every time, this wasn't important enough.
Now with Service desk, this is ESSENTIAL!
Even with the Who's looking plugin, time is lost because hard working people try to solve the same issues, as fast as they can. Collision is inevitable.
So please, make this a priority.
The same goes for setting different default Viewable by, groups. Essential when you need to keep comments internal.

jan