Why is it that...

Sometimes my shop/admin panel takes FOREVER/NEVER loads but at other times it's lightning quick?

When that happens, check the speed of your shop and when you do get into the Admin check the Tools ... Server Info ... and see if it shows the Load on the server ...

Where are you hosting your site? Who is the web-host.

Ajeh:

When that happens, check the speed of your shop and when you do get into the Admin check the Tools ... Server Info ... and see if it shows the Load on the server ...
Yeah it's currently showing all the server information on the page.

schoolboy:

Where are you hosting your site? Who is the web-host.
The webhost is GoDaddy. I ran osCommerce before Zencart and NEVER had any problems with server speed.

There are a lot more things that Zen Cart does than osC and it could be how you have your site setup that is causing the slow down ...

I have a client on a server, not with GoDaddy of course as they are not optimal for ecommerce sites, that has times of:

Parse Time: 0.509 - Number of Queries: 440 - Query Time: 0.22216821788

and less ...

This site has:
Categories: 722
Products: 9,436
Attributes: 127,331

and around 100 to 200+ on the site at a time ...

But the thing is that it doesn't always run slow. At certain times it runs exceptionally well.

When it is up and down like that it is most definitely the server that you are on ...

GoDaddy often overloads their servers and you can try to get moved to a better server with them or look into one of our Certified Hosts who are setup for ecommerce, pph and MySQL needs ...

On the Server Info Page you may be able to see the Load Averages to see what they are at various times when you are slow or fast to see the difference ...

Thanks. If I move to a certified host will I have any problem running my shop in terms of loading speeds?

You shouldn't ... you might talk to the Certified Host before hand and show them your site to ensure handling it ...

I have not seen your site but everything you are saying is the overloaded server symptoms ...

Reks:

The webhost is GoDaddy. I ran osCommerce before Zencart and NEVER had any problems with server speed.

You could be (probably are) sharing a server with a very large number of other resource-hungry sites.

Bottom line is... GoDaddy is completely inappropriate for eCommerce. If you want to do this properly, then you should be with a host that understands ZC, and who has proper server setups.