Personally,
I’m of the opinion that frames should never be used (iframes is a
totally different question, they’re just part of a “normal” page).
There’s a number of reasons why you shouldn’t use frames:

A couple of examples for the developer:

• Difficult to keep the different pages synchronized, especially when it comes to manual reloading by the user
• Hard to push out content. e.g. when a navigation in a frame has neen updated
• Search engines can find single pages and then link to them out of their context

A couple of examples for the user:

• Impossible to create a bookmark for a certain page
• Not possible to save a link that, for instance, goes directly to a product page

You can read more at, for example, Why you Shouldn’t use Frames and even Jakob Nielsen, who maybe isn’t always on the right track, realized already back in 1996 that frames aren’t good (Jakob that, by the way, offers an AMAZING gallery of pictures of himself…).

I read an interesting post by Henrik Torstensson in Internetworld , which was encouraging just to see that someone within e-commerce really thinks.

When
it comes to the technical aspect, there exists such good possibilities
to cache prats of the page for reloading purposes, so server load
shouldn’t be a factor to use frames.

Another
argument people use to have pro frames is that the menu frame is always
ther (for instance, to the left) and doesn’t “blink”, but this is more
of a browser thing than the technical solution. If one, fonr example,
uses a Gecko-based web browser (such as Firefox)
it chooses to get the page one has navigated to, while keeping the
current page visible until the next page is fully loaded, so one
doesn’t experience a white in-between page or a jump, as opposed to how
it’s being handled in Internet Explorer.

From
a web user interface perspective there are a numder of alternatives of
how to emulate frames if one wants to, and the day Internet Explorer
supports the CSS property fixed it will be a piece of cake.

So why do people still use frames? Lack of competence, or are there cases where it is motivated?