Can posting to arXiv ruin your reputation? Arxiv is permanent.  So if I publish something now, that I feel is not quite high enough quality for traditional publication, and people leave a bunch of feedback showing issues with my assumptions or methods, am I hurt for life?  As I understand it, you can't remove something from arxiv, and people can comment on your work.  So, when someone 20 years from now googles my name or domain, they will find the paper and the comments and other undesirables?

At least with traditional publication you have peer review as a filter, which can in part shield you.  Is arxiv really this dangerous?
I think your comment has very important information:


  This paper is just that. It presents helpful information but doesn't develop any ideas or utilize the scientific method.


So, it is not crappy, they are not unbacked claims; it is just nothing new. As long as you are aware of it, and it is clear you are not trying to make it look different, it cannot hurt you.

You can think of this paper as a small review or class notes.

The only thing that may hurt your reputation is if it had very serious mistakes, and you don't address them. To be safe, just ask some of your colleagues to review it, even if it is not a thorough one. They should be able to tell you if it is correct, informative, and clear. And by all means, if it is informative, go ahead and publish it.

Also, ArXiv is not only for preprints of papers. For example, I have seen philosophical dissertations on QM very non technical (a second year Physics undergrad should be able to follow), or another about the story of protein folding research in a certain institution.

Edit:

Regarding your comment:


  but are arxiv posts considered publications for what you're talking about? i could put my grocery list there if I wanted to, right?


ArXiv is not peer reviewed, so the quality threshold is not so high. You can publish not so technical pieces, or sneak a bad article that looks just fine, they don't count as official publications. But, on the other hand, they are better than nothing. Specially if you are at the beginning of your PhD, when you are not expected to have publications yet, your ArXive papers are an example of your capabilities.

No one will use the sheer number of submitted papers, but if you have some fine pieces (for example, a good, brief review of your field, previous research and terminology), can show you have a promising career for, for example, applying for summer schools or extra funding.

Depending on your field, this kind of papers can be extremely useful. For example, in Bioinformatics, most people come from a CS background (programming experts and good Mathematics, but knowing nothing about Biology and Chemistry), Biology (lacking in Algorithmics, Machine Learning, and Statistics), Physics (lots of Maths, but basic knowledge of mostly everything else)... For me, having a quick reference of the basic terminology of other disciplines would save me a lot of time, as I have to look up many simple concepts that would be obvious for, for example, a Chemist undergrad.