Blogs loading slow

Hi Guys,

Could anyone guide me in the right direction I have a wordpress mu site but the blogs are taking about 30 seconds to load.

I have disabled all plugins and it is still the same I have seen a suggestion somewhere to enable zlib and enter a piece of code in the header but still the same.

Anyone have any suggestions of what may be happening I have also optimised database in myphpadmin

but still the same.

I have noticed that once i have opened the blog once and open it again it is faster but for people opening it for the first time it is very slow!