What are the kosher tags: em, i, strong or b?

In the W3C specifications, the EM and STRONG tags made in a section of Structured text -> Items phrases.
EM: Indicates emphasis.
STRONG: Indicates stronger emphasis.
Appearance to display all of the elements of phrases is determined by the browser. These tags may be considered, for example, Text-to-Speech engine to change tone or volume of voice.
\r
At the same time, B and I refer to Formatting -> Fonts and give a clear indication to the browser what font to render the fragment.
I: Renders as italic text style.
B: Renders as bold text style.

i/b — visual design does not make any sense, sort of.

strong has more weight for search engines before the bold, but it can not be abused, of course.

Html5 is about the same. Tags and redefined so that a low — profile selection — strong selection.

EM is designed to intonational accents. In the English tradition such places are italicized. In the Russian language to do so is not accepted, and intonational accent stands out context, construction of sentences. Therefore, for typesetting Russian texts this tag is inappropriate.
\r
STRONG is designed to highlight. And all the rest (of the above), in my opinion, from the evil one.
\r
In HTML 4 this difference, I think, is implied, but expressed wryly. But in HTML 5 is very clear: stress emphasis (check out examples!) and strong importance.

I use i/b in the layout elements, and em/strong is used when you publish posts.

i and b I use for design decisions when using CSS only is impractical (e.g., navigation, image captions, etc. — why devote a span, which is to assign bold, if it is possible to allocate to b?), but strong and em in the main page content to highlight part of the phrase/paragraph/...