I often use Preview in Lion to fill out and sign PDFs before emailing them to various people for various purposes. Normally I let Preview auto-save the PDF, close the file, then drag it into an email message. A few days ago I sent one of these annotated PDFs to someone (on a PC) that wasn’t able to see anything I had entered in the PDF.
I ended up going back to Preview and did File > Print > PDF > Save As PDF.
That worked. I think the Save As PDF step solidifies the changes you’ve made for other PDF readers. I noticed that the text and signature elements were no longer draggable/editable in the version created by Save As PDF.