Reasonable use of Custom Content Types? Should I be paranoid about creating new content types or should I create them for each new content type I come across. 

My particular scenario is having several distinct blogs on my site.


Kitchen Blog
Gardening Blog
Wine Blog


I could have each of these as a standard blog type and just ask the person to remember to set the correct tags. I know I can set up a view to only show each blog with the correct content type but it all seems  a bit messy.

Alternatively I could set up a content type for each based on the blog, then I can set a custom template to look differnt for each blog.

We currently have about 10 content types on the site, could I go to 30 without worrying too much about performance or anything else?
I would not expect any performance problems on a site with 30 different content types. Nevertheless I wouldn't recommend implementing a scheme like you are intending. Should you come into the situation where you have to add a new field or change field/display settings, it will require you to go over all blog-types.

In order to simplify the creation of new content for your authors, I recommend to create shortcut links where the term-id of the blog is passed by an url parameter. You may use the Prepopulate or the Entityreference Prepopulate module, or simply alter the node_form in a custom module.