I have been designing my sites in HTML for years but I see most people designing in CSS now, Should I convert my site or leave it be?

CSS can be a great way of designing your site but many people perfer HTML, Depends what you use really, a mixture seems to work the best for me Using CSS tags to control everything like fonts/colours but still the normal tables etc from HTML

It depends on what you know better i guess. personally i prefer HTML since i understand it a lot better.

CSS can be much more powerful when designing your website, It would pay to learn it for sure!

CSS is much more powerful and accepted but I still do it in HTML because I do not know CSS that much. But I mix a little bit of CSS layout for my menus and the codes of my pages are so mixed up and confusing.

Go with using CSS for layout. There are many benefits one being that you can ultimatley change the whole visual look of your website from one stylesheet.

The others being that from separting content from design, search engines spider your content better. Along with using semantic mark-up i.e if its a header mark it up as a header in the code. Your website should be viewable to all text-based browsers and accessible for disabled users.