Two main differences between oldest version:
1) Plug-in sets one special cookie for identifying the user. Users, flooders, spammers etc. who have cookies turned off, will not be taken into account. This should solve problems within intranet or proxy users who share the same IP.
2) File rewriting operation is optimized, so it uses now not PHP locking procedures, but system's RENAME operation which is more faster.
Users who have previous version, should follow update procedure inside README file. The main difference is that you need to create separated shared directory within your forums. This directory could be used further for another plugins (for example, for Avatars plugin which is mostly done and is on the way).
Download the package, as usual, in our Downloads
On our forums, we have reset the "Most users ever online" - so don't ask why we have so small amount of visitors now. We don't actually believe that sometimes we have 53 users instantly online and expect that it was some kind of lack of the plugin.