double-word sentences, 忽。。。忽，时。。。时。。。

Ok, I'm not going to go over the ones you should know already like

又。。。又。。。 - 她又笨又好看，去找找！

or

有。。。有 - 这儿的学生有好有坏，大多数没用。

I'm going to go over the ones I'm less familiar with.

忽。。。忽, this feels like HSK grammar I saw once in another lifetime. It has this 'oscillation' usage, 他的病情忽好忽坏。

From nciku:

配对用在两个意思相反的形容词或动词前面，表示一会儿这样，一会儿那样

忽走忽停。

Know this.

This is similar to the use of 时。。。时。。。, with it's 'flickering' or 'going back and forth' between two poles.

又。。。又 does not have this kind of usage.

Ok.

nciku also puts this the 时。。。时。。。 usage like this：

两个“时”字前后连用，相当于“有时……有时……”“一会儿……一会儿……

and the 一会儿。。。一会儿。。。 usage like this:

now...now...; one moment...the next...

(which I think is about right)

Their example

天气一会儿晴一会儿阴。 (Their translation kind of sucks, but you get the idea.)

I think you get the idea.