I've always viewed this as a plus for tabs. Personally, I think two spaces is too small. If I'm looking at someone's code and it's hardcoded to two space indentation, I'm screwed. But if it's using tabs, I can set it to whatever I want. Some people like 2, some 4, and some 8. I prefer to use tabs to denote logical indentation, and then space for formatting. But not many people agree with me, so I usually just use spaces.
Generally I agree, but for the pedantic there are other issues. Tabs at the beginning of lines aren't a problem. But, for example, it's common to see multi-line declarations of, let's say, a hash where each line looks like this:
key <tab> => <tab> value
This might look perfectly fine for someone using 8-width tabs, but it will most likely be screwy for anyone using 4-width tabs or smaller. The tab's location is calculated as the distance where the cursor position modulo the tab width is 0.
E.g. one key is 2 chars long and another is 5 chars long. You tabbed it using 8-width tabs. Looks fine. If someone loads it with 4-width tabs, they see the two lines aligned differently.
I've heard all sorts of arguments for and against, but in the end it only matters that you consistently choose only tabs or spaces, and that you use whatever header-settings your IDE provides to enforce the decision across all the coders, e.g. for emacs:
Upvoted, but would like to add to bazookaaa: easiest way to change this habit is to set your editor to insert two spaces when you hit the tab key, that way you don't have to think about it ever again.
Two spaces are always two spaces.