I'm using wordpress and I have too many categories about 600+ and I find it a bit slow to load when creating a new post. Is there a way to cache the backend?
You can use gears. If you are using the new wordpress 2.5+ look in the top right hand corner and you will see a link that says turbo. Click there and it will instruct you to insatll gears. Once geras is installed reload your browser and click there again to activate it. Hope that helps.
I don't believe it has something to do with the categories that you have when you speak of loading time. It must be the plug-ins that you have installed in your Wordpress. I have quite a lot of people who removed some plug-ins especially those that were not used or of no use at all and they had their loading time turbo charged since. Also you can always try to remove unnecessary images or Ads that you have which are not earning you money. You can also minimize the use of Videos from YouTube because they really add up to your site's loading time if you have a Wordpress. That should do it.
I can see it in the right situation. Perhaps someone is using wp to run a movie streaming site, article directory, or ecommerce site it could very well be necessary. Perhaps maybe only 10-20 categories and the rest in sub categories, but this would still mean things run slow. I still suggest running gears, it really speeds things up.