Filenames: I believe it's like 260ish chars and that is a windows limitation for ordinary filenames. You can use a special filename suffix on I think windows 2k+ and later to indicate a unicode filename which can be up to 32k characters long so you're both right
Windows explorer does it correctly, and some other apps that don't do it right appear to work with longer paths because they set the current working directory and then use only relative paths under 260 characters from there... The FTP with paths all over the place on different drives has to use full paths though.
The problem is I'm not sure how hard it would be to change over all places where a fixed width is used. The good news is the most common place is inside the path structure and it doesn't assume 260 chars. Inside ioFTPD itself the max VFS length is 512 so in some cases you can already fake things out by mounting top level physical dirs deep inside the VFS...
Full unicode filename support such as isteana wants is really hard with this codebase as I've pointed out in the past. However, longer filenames is much easier because the code would still be compiled using single byte characters and thus won't break things all over the place. I don't plan on doing anything about this problem right now though...
pion: site change admingroup doesn't create a logentry. I agree, seems like it should and I'll add one.
Viewing admingroups: I changed the default "site uinfo" somewhere around v6.2 when the default group for newly created users started using the first listed admingroup of the creator. If you haven't updated that file you might want to as it shows a list of all the admingroups in order for the user now... It's a bit tricky to get the order of the entries in the admingroup correct since you can only add/remove entries. Thus to get a newly added admingroup to the front you need to remove all existing entries and then add them back. Kinda sucks, but it's the same problem the normal group list has as well and the first entry there is important since new files/dirs get that group by default... ioGUI will also show groups and admingroups but there isn't a good way from the user editor to tell which are the first entries.
site take/give: Those are not internal ioFTPD commands, the script needs to create a log entry.
site adduser/deluser: These commands appear to update the group user and slot count correctly. Are you using these commands or a script to do it?
hukker, noelek, pion: I think all 3 of you are using nxmydb and the libsql libraries and seeing crashes pretty often. Since I'm not seeing that elsewhere and you all have it in common I suggest you try not using it for a couple of days and see if things are otherwise stable... It's probably a simple bug but at least we would know where to start to look.