I told you yesterday that evasi0n7 was released by Evad3rs without the developers of tweaks and plugins for Cydia to have the opportunity to prepare his creations for iOS 7, and this generates many problems for users. At first you will see the error above in Cydia: Failed to fetch http://repo666.ultrasn0w.com/./Packagez.gz HTTP/1.1 404 Not Found and to solve it navigate in Cydia to Manage/Sources and delete the Dev Team repo if you don't need ultrasn0w.
Apart from this problem, many tweaks will tell you that they cannot be installed in your terminals because they are not compatible with iOS 7, and here I think you understand the problem yourself. Other possible errors, such as POSIX: operation timed out, appeared during the loading of the repos are due to the very high load to which the servers are subjected, but the problems will be solved in the following days, including those related to incompatibility.
