Great plugin -- very handy! I've put it to use immediately. One feature that would be extremely helpful is the addition of a toggle to display instance counts alongside each entry in the text areas. What I mean by this is a count of how many times each individual IP, email address, or URL was used in the current batch of spam. This will give a better indication whether a specific IP or email address was a one-time spammer or a chronic/heavy spammer/repeat offender. This will help in deciding who to permanently blacklist and/or IP ranges to set firewall blocks on.
So for example, there could be a checkbox labeled something along the lines of "Display offence counts", and when enabled, the text box output would include the counts in brackets, sorted descending by offence count, then ascending by IP/email address/URL -- e.g.:
IP addresses: 180 109.230.216.xxx (76) 85.222.103.xx (6) 178.137.142.xxx (5) 208.77.101.xxx (5) 107.20.251.xxx (3) ...
e-mails: 313 firstname.lastname@example.org (7) email@example.com (5) firstname.lastname@example.org (2) email@example.com (1) firstname.lastname@example.org (1) ...
(Note: I've included some anonymized sample output above for IPs/email addresses, but didn't include output from the URLs for obvious reasons)
So from the example above, we can see that in the current batch of spam, 188.8.131.52 would be worthy of blocking since it offended 76 times, as opposed to ones further down the list which only did a single time.
I had some spare time, so I went ahead and made the additions to include this functionality. I noticed in the code that you've planned for stored/changeable options. The modifications I made will need one additional option added ($display_counts). I've temporarily set a hard default of 1 for it on my end while testing, but ultimately it'd be set to 0 and toggled by the user once you've added in the UI & handling for that.
Here's the modified function (Pastebin'd as per Forum Rules): http://pastebin.com/5vMuP99r
It'd be great if you could incorporate this into the next version of the plugin.