What they've said is correct. 'ge' is not used for everything. 'ge' is simply a generic measure word. Almost everything has its own specific measure word. Locals can judge a foreigners Chinese ability by how many correct measure words they use. However, if you just you 'ge' for everything, Chinese will understand you and its a lot better than using none at all!

it depends. to some extent, "ge" is similar to "piece" in english in that they are restricted in context.

well there are lots of such words,such as "zhang" yi zhang zhi (a piece of paper), "zhi" yi zhi bi(a pen, a pencial).... "ge" is not for everything, but when you say "ge" people also can understand you

一 瓶-ping 水 一 张-zhang 纸 一 座-zuo 山 一 台-tai 电视/冰箱/电脑 一 支-zhi 笔 一 辆-liang 车 其他的都可以用个了好像

"ge" is okay to be used with a person, an idea, a hat, an hour and some others. "ping"瓶 is for a bottle of wine or water. And here are some usages about this kind of words 中文数量词的用法，常常和归类有关。有脚动物归成一类（人除外），以「只」数之；长条形的东西以「条」数之等等。归类自然得寻找共同的表征，也就是寻求规律。当然，老祖宗在发展数量词的过程中，归类的工作没做得非常科学。「颗」与「粒」怎么区别？大体来说，粒指的是颗粒状中较小者，颗则大小通用。粒可大到怎样的程度？我们说一粒苹果或一颗苹果都可以，显然粒至少可用到大如苹果者。不过比苹果稍小的心脏不能以粒来数（至少国语如此）。另一极端，在闽南语中，我们常说一粒西瓜，不说一颗西瓜，而用国语，则说一个西瓜，少说一颗西瓜。我相信应规律化之趋势，数量词会愈来愈简化.