Performance issues

[jjk]

Some additional comments
On your homepage you are still loading three copies of jQuery of which two are different versions:
...ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js
...keyboard-centrum.nl/templates/kbc_1_sidebar2012/jquery.js (1.6.4)
keyboard-centrum.nl/modules/mod_jlv_facebook_sidebar/js/jquery-1.7.2.js
You seem to be working on your site while I type this, because the jQuery I see has just changed. Now I also see:
...keyboard-centrum.nl/modules/mod_slideshowck/assets/jquery.min.js (1.7.1)

You should load only one version of jQuery. Otherwise it's likely that there are javascript conflicts which can result in all sorts of problems.

If you are using the Firefox browser, you can see such issues and many more if you install the Firefox browser plugin 'Firebug' available here: https://getfirebug.com/

Personally I prefer to use the VirtueMart jQuery instead of loading jQuery from Google, because sometimes the Google api service is slow. Another disadvantage is, that you can't work on a local (xampp) copy of your site on your laptop without being connected to the internet.

As Milbo mentioned already, VM 2.0.26 works better with Joomla 'Conservative cache' (Do not use the Progressive Cache!) enabled than VM 2.0.24. So you might consider to update to latest versions of Joomla/VirtueMart (test on your xampp copy first of course).

Btw - just for comparison. If you go to the VM2 shop described here: http://forum.virtuemart.net/index.php?topic=110005.0
you will see a fully working VM2 shop which currently also has approximately 600 products and is running on a cheap shared server with cache still disabled.

[fmlk4u]

Just clicked on your provided link and page loading times were looking normal. Perhaps YouTube was slow when you were testing. Just curious - which plugin do you use for embedding the videos?

Looking at your shop with Firebug, it shows two missing images:
...keyboard-centrum.nl/templates/kbc_1_sidebar2012/images/vmgeneral/next_16x16.png
...keyboard-centrum.nl/templates/kbc_1_sidebar2012/images/vmgeneral/backgrounds.png

Hello, w.r.t. the template: I don't have a vmgeneral subfolder at all. I created the template with Artisteer. W.r.t. the plugin, I use the K&K YouTube Plugin for Virtuemart