as much as I figured out so far, I only have the ability to filter stuff I want to see only, but not the other way round (which I need far often) is filter away stuff I dont want to see and leave the rest as it is.

For instance we have a Guest title for people who dont raid. Now if I wanna see all people who do raid I seem to be out of option, because so far I only managed to filter for only Guests to see only them or to filter for Members to see only these, but which leaves out the guildmaster, classleaders and officers. So just erasing Guests out of side like the "Hide Alt" button would be nice.

tried some ! operator as well, but the filter box seem to except only the text string.

There are some operators that can be used in the memberslist filter box, but that does not currently include a not equal operator. I'll add it to the todo.

For completeness, and because it's not in the docs yet, these are the supported operators:
<no operator>: Substring match
=: strictly equal
>: greater than
>=, =>: greater than or equal
<: less than
<=, =<: less than or equal

All of these work on number fields. Some fields, like guild rank, are number fields internally. All operators should work on those if you provide the number instead of the name. For date fields, all operators should work, but the flexibility of the date parsing varies heavily per browser.

Added:

!=, <>: Not equals
~: RegExp match
!~: RegExp no match

Added the regexp ones because I was at it anyway and they're not too hard to add. Flags are not supported, since that would require more complex parsing of the filter box than I do now.

uhh I cant get any of these to work. Can I get an example please?

Lets say I want everyone shown who has not the Title "ALT" or "Guest".

tried entering tons of stuff, but nothing even got me some results.

figured it out, though the Title I liked to filter still user the ranks is a only convinient for the admin who has a change to look into the db for the correct rank <-> title correlation :-P

So you might reconsider changing that.

!~[5,6,8,9]

worked fine in there.