does anybody know how long it takes the universities usually to decide about an application ? I applied (1 month ago) for 3 programes in the UK starting in spring, but did not get any response yet.

It varies a lot from one uni to another... but I'd say that one month to two is the avarage time...

do they usually inform you, when something is missing in your application ?

(For example, when something you send by post was not received or anything like that ?)

I wouldn't know 'cause I didn't receive anything like that... but I did receive notices saying my application was complete, so I believe they let you know if anything is missing.