I use the "FrameMaker primitives" that Bill Briggs created. I added them to AutoText (you do use the AutoText plug-in, right?), so I can just select the piece I need from the AutoText menu, type the text, and then add the next piece. Some final alignment at the end and it's done. Using the combination of Bill's flowchart pieces and AutoText, I can *complete* a simple flowchart with about twelve pieces in around five minutes.
I also use Visio for many types of drawings. To keep the quality, I export as a vector format: usually PDF (on the way to EPS), but occasionally WMF. Remember that the Export to EPS option is (and always has been) horribly broken in Visio. WMF is a vector format, but it has many problems that I won't get into here. (WMF is still a handy format sometimes, because you can give it to marketing guys to include in PowerPoint. Double-clicking the WMF in PowerPoint makes it editable--at which point it's not your problem anymore and the marketing guys can tweak the colors and fonts happily all day.) For best results from Visio, save to PDF, crop in Acrobat, export as EPS with a preview. It's a bit of a chore, but worth it for some things. One hint that really helps: put all your Visio pictures for one project in a single file.