As a word, an interjection, a qualifier, i started using almost a decade ago... cause i started figuring out nothing was either one way or another... nothing was extreme. everything had a "ish" factor. there are always exceptions to the rules. and what might be everything to one person, is just "ish" to another. there are planty of fine usages of the modifier. it helps one get out of telling the truth without lying... "your band was amazing!... ish." etc...

It looks like these days "ISH" is also now being used frequently among the hip under 40 in a mostly sarcastic way;
For example; "That party was the best ever! ...ISH". which meant it really wasn't fun at all.
or "You look really slim in the dress my dear. :) ...ISH". ( she whispers so her firend doesn't hear)
or "Guess what, our boss just told us we have to stay at work 4 more hours! FUN! ...ish"

You get the idea.
Though it hasn't been only negative;
For example when people complain about how hard they have it cause they didn't get the watch the wanted
or they didn't get that gift they wanted. But it's just something i'd always say sarcaticstilly but being honest that when things suck, they could always be worse :P
"Life's Hard! .......ISH ;P" and then everyone'd all laugh humbly how lucky they really be.

Also it can also help take the extremeness out of every situation... not everything has to be only one way or another....
everyone is a little right and a little wrong. and surely the chances are i'm right, but only....
and well enjoy some slanted slang that you might find useful.... ish ;)

(Someone found my defintion of "Ish" on
http://www.urbandictionary.com/define.php?term=ish
i knew i should've copywritten it or something!)

(Oh! and there's a production company that makes that Paris' hunt for a BFF show, called you guess it "-Ish Productions" i should sue...! :P)