The addition of ticket relationships is very useful for tracing through the tracker.
Here are a few ideas for enhancements to the current implementation:
1.) In the "Related tickets" section, show the current state (Open, Closed, etc.) of the ticket being referenced. This would likely necessitate a one-ticket-per-line arrangement or something else aesthetically and functionally pleasant.
2.) When modifying the relationship, a ticket history entry (with optional comment) could be created. The history entry for the relationship change should be entered for both tickets. Considerations:
3.) One more level of granularity for the relationship type - "Depends On" and "Required By". A ticket X "Depends On" another ticket Y if ticket Y must be implemented before/simultaneously with ticket X. "Required By" is the same relationship viewed from the other side.