Does the comma go before or after but in a sentence?

It goes before the but.
Ex. I really liked her, but she did not like me.

How about both?

I wanted to jailbreak my iPhone, but, after realizing I had no idea what that even meant, I asked Fluther and life became beautiful for me again.

There are very few absolute placement rules in English. You can’t generalize which side of a certain word the comma should fall on.

One way to get around the whole grammar thing is to refer to everything you write as “stream of consciousness prose.” It also releases you from the bounds of capitalization and punctuation.
For general usage, though, I would agree with Chawk. Too, many, commas, makes, a, sentence, trip, over, itself.

but is a conjunction word, so the comma will always go before it when used in that capacity. When using it as robmandu did, you wouldn’t put a comma before and after- you would use a semi-colon before and a comma after:

I wanted to jailbreak my iPhone; but, after realizing bla bla bla…

And you would typically use a “fancier” word then but like however or moreover

@lefteh: You can, and style guides have done. Jballou’s suggestion is the best option.

robmandu’s example uses a comma after the “but” only because he inserted the adverbial prepositional phrase “after realizing I had no idea what that even meant”. If that phrase were removed, the comma could only be before the “but”: “I wanted to jailbreak my iPhone, but I asked Fluther…”

@Harp, you captured my intent perfectly.

James Matthew Wilson presents this example:

These claims for the difficult craft of verse are valid insofar as they go. It takes work to learn to hear meter as it does to write it. But, like grammar, once one gets the hang of it, it becomes very easy.

I was totally going to answer this question, but you guys have, like, totally covered it.

@lefteh It is much better, in general, to start off knowing and following the rules before you start freelancing. It’s like school figures in figure skating. The grounding gives a base to work off of.

do a comma go before and