The quality of free software tools available for GNU/Linux has improved enormously in the last few years. Unfortunately there is one glaring exception: there is no decent application for editing and saving PDF forms. When working with very long forms, which may require more than one editing session, the ability to save the form is critical. It is also nice to archive them in an editable format. This is not such a problem with short forms since you can just edit it and print it to a postscript file if you want to store it.
In terms of open source PDF viewers, KPDF (soon to be Okular) is the best offering in my opinion. It is extremely fast and has a complete set of features for a viewer. Unfortunately, it does not support forms at all.
Even if you only want to edit and print the form, the only decent alternative is to use Adobe Reader. The Linux community came very close to having an open source alternative with the forms-enabled branch of Evince, the PDF viewer for Gnome, but development on this branch seems to have completely stalled. I was able to compile it from source following the instructions on the site and I was indeed able to edit forms. It did not seem to be capable of saving the form after it was edited though.
Even Adobe does not offer an application capable of saving edited PDF forms in Linux (not even a commercial product). I did eventually find an alternative proprietary solution in a program called Cabaret Stage, a Java-based application for working with PDF forms. There is a freeware 32-bit version available for Linux that can edit and save PDF forms. Unfortunately, the memory footprint is huge and it is painfully slow (even on a relatively fast system, a dual-core Athlon X2 3800+ with 1.5 GB RAM). Compared to KPDF it is glacial, but it works for now. Hopefully one day native form support will be standard in Okular or Evince.