3- The user who solved the maximum number of problems during all Codeforces contests is Egor, he solved 453 problems.
4- The user who made the maximum number of successful hacks during all Codeforces contests is Egor again, he made 358 successful hacks.
5- The user who participated in the maximum number of Codeforces contests is PAG, he/she participated in 130 contests.
7- The user who made the maximum number of unsuccessful hacks during all Codeforces contests is sdryapko, he made 154 usuccessful hacks.
8- The user who used the maximum number of different programming languages during Codeforces contests is K_operafan, he/she used these 11 languages: Io, Befunge, C#, Pike, C, Ruby, Roco, Tcl, C++, Java, Cobol.
9- The user who solved more than 50 problems during Codeforces contests with the maximum percentage of first-submission-accepted problems is KOTEHOK, he solved 57 problems and 54 of them were accepted from the first submission, with percentage ~ 95%.
10- The user who made more than 50 hacks during Codeforces contests with the maximum percentage of successful hacks is vepifanov, he made 56 hacks and 52 of them were successful, with percentage ~ 93%.
P.S. The above statistics is calculated for all contests before Codeforces Round #131, and unofficial participants are counted, but virtual participants are not count, and this information might not be 100% accurate.
Edit 1: Number 8, 9 and 10 are added.
Edit 2: An always updated version of this post can be found here.
Edit 3: This page now shows the top 5 in each category, but in different order and number 3 is new one. And can display statistics for a single user also.