it is an upgrade from an old server (1.8.9 on centos5), I've installed centos6.3 from scratch, transferred and upgraded the database to mysql5.5.
everything(data gathering/triggers/notifications) seems to be working but the web interface is a slower then before and screen generation in particular is very slow and sometimes times out.
I use chrome(20.0.1132.57) on Linux as my default system and I'm a logging in as a super-administrator and at first I was sure it was the system so I've tuned every thing I could think of with no luck.
(my mysql was already tuned, I've installed APC- php caching and tried with a clean browsing history)

then I tried to login to my zabbix frontend with an internet explorer on windows and it was working blazing fast. I've also tried with firefox on linux with the same fast results.
Finally I've tried to login with chrome(20.0.1132.57 too) on windows with the same slow results.
all of those browser test without changing anything on the serve side.