In other words, this site is pretty safe...
Not all of us are geeks. Sometime very simple tasks require a little bit of explanation.
With Stanza (acquired by Amazon) and the Kindle app being used to read books on the iPhone, it makes a lot of sense to expect those applications to be able to read PDFs.
The funny thing is that I have seen users actually convert their PDFs into the eBook format just to be able to read them on the iPhone.
Apparently some users like the way eBook readers let you browse through pages. One of common practice is to convert PDFs into eBook formats using for example the Calibre Application.
Now I hate being the one breaking the news but the iPhone actually supports PDF. What it means is that the real problem is not to know how to read PDF, but more on how to transfer or have access to your PDFs on the phone.
I have looked into different solutions, and the one that worked for me (mostly because it is free) is Dropbox. This app lets you sync documents between your PC/Mac and the iPhone through their site.
If you have an unlocked phone, you can always ftp/scp the files which would work, but the interface of Dropbox is pretty nice.