This is how my ratings go.
1-3 piece of Crap.
4-5 Rubbish But has at least 1 redeeming factor.
6-7 Average
8 original and brilliant but is let down by one or 2 factors
9 almost perfect it does exactly was it says and almost impossible to predict and is structurally stable but is missing something that would have made it perfect.
10 masterpiece, perfect in almost every way .

Ghost in the shell, Zetman and Domu are the only titles i have given a 9.
I've never given a 10 so far but i still hope there is a manga or an anime good enough to deserve it.

[img]http://i572.photobucket.com/albums/ss162/westsiders2/Signatures/comicsigcopy2.jpg[/img].
http://westsiders2.deviantart.com/

Probably because they really moved me, touched me, impressed me, etc., on a certain level that was awe-staggering and so on. 🙂 However, just because I gave it a 10 at a certain time, doesn't mean I'll always give it a 10. People change all the time. 🙂 This also means I've harshly demoted certain titles like from "10" to "4" and so on.

Edit: It also heavily complicates things that I read a lot from different genres and categories, so I often have trouble giving a proper rating or even a review.

I rarely give 10's, but that's because I've been reading mange since I was like...7-years-old.

There are some series that receive 10's and I can't agree with the rating for the life of me. But I also understand that my taste is my own. Obviously, everybody's not gonna like the same things. So I think that people give 10's because those particular series' just suit their taste 😃

I'm a bit of a drifter between two countries

I have 300 series on my completed list and out of those, I've rated 12 of them as 10. I'd say that isn't very often. I used to never rate any as 10, because there's no such thing as perfection. But then I got tired of rating stuff as 9.7, 9.8, 9.99, etc. Much simpler to just put them all as 10.

I don't rate based on art/story/etc. but just on how much I liked the series. Obviously art/story/etc. plays a part in how much I like a series, but I would still rate it as 10 if I really liked it even if art was a 7.

If I rate something as 10, it's something that I would still enjoy after reading 3+ times and one of the first series I would recommend to someone in its genre.

I rate pretty much everything I add to my complete list (and some on my reading list). westsiders2's rating description pretty much perfectly encapsulates how I rate as well, but when it comes to 10s there are some differences on my part: I don't actually have to consider a manga a MASTERPIECE in order to give it a 10. As long as it was a masterpiece for me it's good enough... This reflects the fact that I rate everything mostly for my own reference: What do I want to re-read? Which mangaka do I want to keep an eye on? etc. Something might not be a genius piece of work, but it it's something that's perfect for me, that is, if it ticked off all of my boxes, it will get a 10. I mean let's compare it to movies... I might not think a rom-com is comparable to a Stanley Kubrick masterpiece worthy of international aclaim 😛 but I will still give it a 10 if it satisfied what a rom-com should satisfy and most importantly, if it satisfied me. I guess what I mean is that I judge a manga on its own merit and for what it is meant to be instead of trying to see whether it compares to a true masterpiece. As such I will not hesitate to give a lighthearted shojo or a smut title a 10 if it really deserves it, based on what it is meant to be and what it tries to accomplish. (e.g. for the shojo: does it make me feel good, keep my interest, make me laugh, for the smut, does it turn me on??)

Well, I'm quite generous with my rating.
It's not like I give out 10's to every series I liked, but I do rate high.
For my personal rating system, 5 will be THE lowest I give. 5's are the ones I didn't quite enjoy or there was just a really flawed factor that's not to my taste. 7-8 is the average rating for me. I don't feel the need to use 1-4's. That's just MY opinion.

10 for me means I really enjoyed it! I don't need it to be my absolutely favorite manga, it just has to be very enjoyable. :3