If you're searching by IP, or getting all IP addresses used by a member, it should be possible to see that the IP address has been used in PMs. I think it should also give the date range that it was used, but no more information - the title, recipients and contents should probably remain confidential, and it shouldn't be possible to join the PM from the IP lookup. There are some members who join and just send PMs, and it would be really useful to be able to see that they have used the same IP address as another banned member, etc.

I like the way 3.4 did it.

Host Address for xxx.xxx.xxx
IP address resolves to

Members using that IP when REGISTERING
Members using that IP when POSTING
Members using that IP when VOTING
Members using that IP when EMAILING
Members using that IP when VALIDATING

This IP address was also found...
message_posts
moderator_logs 
member_status_updates
(etc.)

All with IPs and dates.

Yep, it's also missing error messages. I'm still waiting patiently for them to add in these two things that were already being included in the IP listings for 3.4. 

There are several enhancements to the IP tools in 4.1.17.