Personally, I tend to download pdf files (with wget) and view them locally rather than opening them directly. Once you've downloaded it, it's obviously much quicker to open it locally rather than re-downloading it every time you need to refer back to it (well, I suppose it doesn't matter if you never read it again). I also use pdftotext to convert to text for easy grepping (btw, the -layout option will preserve the layout of the text as much as possible, much better than the default output).
As for viewing (in a GUI),
xpdf is light and pretty good. The download page has both source and binary packages. Check your distro packages before you download it though, you may have it already.