Even minor problems seem (to be ) important.

They seemed (to be) good at reading.

What seems (to be) the trouble?

都可以省略。不仅仅是 seem，其他系动词也可以。

一、英语中，seem, appear, prove, turn out  等系动词后，可以接 to be + 表语：

There seems to be a storm tonight. 今晚好像有暴风雨。

The boy seemed to be ill. 这个男孩好像病了。 

He appears to be angry. 他似乎生气了。

The plan proved to be useful. 这个计划证明是有用的。

The weather turned out to be fine. 天气结果很好。

二、在这些系动词之后，to be 都可以省略：

There seems (to be) a storm tonight. 今晚好像有暴风雨。

He seems (to be) sad. 他似乎很伤心。

He appears (to be) angry. 他似乎生气了。

The news proved (to be) false. 那消息证明是假的。

The man turned out (to be) a thief. 那人结果是个小偷。