In short, flag weight is a measure of how reliably you flag content. High flag weight is good. It can range between 0 and 750. It increases if your flags are positively reviewed. The more flag weight you have, the more you can flag, and the higher the priority of your flags is. High flag weight is rewarded by a Deputy (500) or a Marshal badge (749).
AFAIK only users with more than 200rep are taken into account. The rest don't count yet as full site members. If you go to http://stackexchange.com/leagues/29/ you will see in the right side bar that only about 10% of the users have 200rep or more, which explains the factor of 10.
Flag weights above 500 are by design displayed with four digits after the comma. Up to a weight of 500, a "helpful" flag increases the flag weight by 10, but for higher weights, the increase for a helpful flag is less than 10 -- IIRC, it is exactly 1 for a weight of 625 and 0.1 for the maximum flag weight of 750. Because of the somewhat counter-intuitive ...
As stated in my comment(s), marking a question as a favorite, by clicking the star below the arrows for up- or downvoting is a solution. Later these can be listed by the user. This a good system to show at the same time that the question (or an answer to it) was particularly valuable for a user.
the boxed number shows the positive votes received by your answers. You can see it by placing the mouse cursor over the number for a couple of seconds:
this is what happens after hovering the number 4.
In your screenshot the user has never answered any question, so all tags have zeros. He gained rep only with questions, not answers
It seems that the Imgur system, which is now used for the "Uploaded picture" option in your profile page (see this link), does not support .png with an alpha channel. Every time I've tried to upload one, it was rendered with a white background on TeX.SE:
I was misled by this 2008 discussion about Gravatar's discontinued support for .png with an ...
This is no bug, it is a normal behaviour. Quoting the meta.stackoverflow.com post "What is flag weight?":
Why is my flag weight not an integer?
Because flag weight above 500 does not increase in a linear fashion,
decimal places are shown for precision purposes and to show you how
your flag weight is changing.
User profiles are granted as much liberty as possible, but there should be some common sense in terms of the content being posted there. User profile pictures especially, since these make their way into the mainstream site content more readily than the description (in the user flair).
If you have reasonable doubt as to the social acceptance of a user ...
It seems like negative rep changes are not displayed in these graphs, it'll say "This user has no recent positive reputation changes". (Find a question with a negative score on http://meta.stackoverflow.com and go to its asker's profile to see that.)
But still, you have a point because people don't immediately know that only positive rep is displayed You ...
Status completed, issue solved:
Yes, I can definitely see some confusion here, the format will use a :
instead of a - in-between the date and rep next build. – Nick
Craver♦ 2011-11-26 10:49:13Z
at https://meta.stackexchange.com/q/113693/171937 (has been deleted as solved).