Cartoon characters, such as Mickey Mouse and Snoopy, are still popular.

这个句子中such as...是限制性修饰语。没有这个限制性修饰语，句子的读起来是含糊不清的：Cartoon characters are still popular.

非限制性修饰语通常有逗号隔开，但也可以不用逗号。但是限制性修饰语是不可以用逗号的。所以，网友自己写的这个句子用逗号是错误的。除非主语改为Some cartoon characters, 这样的话，such as就是非限制性修饰语，用或者不用逗号都可以。

Cartoon characters, such as Mickey Mouse and Snoopy, are still popular.是对的。

1. such as位于句尾可加或不加逗号，加逗号常表语气停顿。例如：

Do avoid potentially contentious subjects such as religion, sex or politics.一定要避免可能引起争议的话题，如宗教、性和政治。《柯林斯高阶英汉双解词典》

You have to type in commands, such as "help" and "print".你必须输入命令，例如“帮助”或“打印”。《柯林斯高阶英汉双解词典》

2. 若such as短语插在句中，可加或不加逗号，若加的话则前后都加。

Wild flowers such as orchids and primroses are becoming rare. 兰花和报春花之类的野花越来越少了。《牛津高阶英汉双解词典》

Of course, using some of these proxies, such as race and gender, might violate the Equal Protection Clause of the Fourteenth Amendment to the u.S.（美国当代英语语料库）

   such as 表示“像.....的”（可以与 like 互换），是介词短语，作后置定语，这种用法的 such as 前后都不能用逗号。例如：Boys such as John and James are very friendly. ( 摘自 Collins English Learner's Dictionary by D.J. Carver,etc. 1974) 像约翰和詹姆斯这样的孩子对人是非常友好的。

     such as 表示“例如”，其前面可以用也可以不用逗号。例如：Corrosion is an electrochemical process by which a metal, such as mild steel, returns to its natural state, such as iron oxide or rust. 腐蚀是金属（例如低碳钢）返回其天然状态（例如氧化铁即铁锈）的电化学过程。（摘自赵振才编著《英语常见问题解答大词典》增订版第五版p.1427）Mineral resources such as iron, gold and magnesite are abundant on the peninsula.在这个半岛上矿产资源，如铁、金、菱镁矿等是很丰富的。（同上）