Several people use MSN since long years ago, and saved hundreds and hundreds of chat logs, and hundreds of contacts.
My suggestion would be adding a small opcion within the Chat Logging configuration panel in the option menu to
allow Messenger Plus! to update all former chat logs to fix a new 1 Log per Contact. (instead of actual 1 folder per contact) Each contact's logs would be stored on a single HTTP file (txt files dont allow too much text on them) so for looking for specific conversations with a contact could be made easier (no need to browse around half a dozen files
)
I'll comment my loggings distribution as an example for the first suggestion:
in my defined chat logging folder (currently D:\My Docs\My Conversations) i have a folder for all chat logs from each month (created automatically by Plus!) from january 06 to december 07, then i have a folder named after my hotmail adress, and within it i have months folders from dic 05, some more months from '06 (probably due to a change in the chat logging configuration that lead to two separate December 2006 folders, for instance) and all folders from 2008 and current 2009.
Indeed, i considered that the new option for creating a folder per Contact instead of per month would better organize my chat logs, but.. what can i do with all my older logs? Again, we are talking about years and years of chat logs, organizing them "by hand" would take weeks.
But with an option within Plus!, i dont know, running a script or something that would read all http/txt files within the Conversation folders and reorder them to fit the new Contact HTTP Files setting, this could be made at PC-speed (won't take more than a few secs probably
)
If asked to update logs to contact HTTP files, after listing all contacts, all logs from every contact should go through a similar process: getting ALL text from all files corresponding to one contact, and reorder them with one single file using the headings to get them chronologically ordered.
In that way, we end up having ONLY ONE single HTTP file per Contact, no folder and subfolder schemes, and much less (but bigger) files.
Even old txt logs (or not old; i myself still have txt logs setted to avoid having both HTTP and txt logs) could be updated in this way, as they still include a text heading for each message sent. (that could be used to make them fix a chronological order within the HTTP file)
To conclude, with this option (dont hit me
i know its pretty complex
) all former txt and HTTP logs that currently form an incredible number of scattered files within your Plus Logs folder, would be instantly simplified and reordered =D
to clarify, what i mean about the "processing" of texts is that they should be REORDERED at the moment; not just putting in 1 single file all text from the older log, then all text from the 2nd older log and so on to "stick together" all logs from every single contact (this could be done indeed as a quick option, but won't be as precise as my explained process 
/ 
