I have a workflow for preparing (including cropping) vector images for inclusion in LaTeX documents that I'm pretty happy with. (The cropping tip near the end of this post is probably the most useful thing I have to say.)
I produce documents via pdfLaTeX that contain numerous electronic circuit diagrams. I create the individual circuit diagrams with XCircuit. They export as postscript files. Then I convert them individually to pdf's. I use Adobe Acrobat's conversion capabilities, it provides a handy convert-ps-to-pdf option when I right click on a .ps file. But I can just as well convert with something like Gsview.
If my document is to contain say 5 individual circuit diagrams I import all 5 individual (now pdf) circuit diagrams into a single inkscape page, using the File>Import... menu option. The 5 bare circuit diagrams are scattered about the page ready to be edited. In my case I usually add some text to each circuit like component values, or add some arrows with labels pointing to some particular feature of the diagram that I want to highlight. The plugin TeXText is great for using LaTeX markup for text in Inkscape.
I save the page as an Inkscape SVG that I can re-edit in the future if needed.
But then I'm ready to prepare each of the 5 polished circuit diagrams as its own individual pdf for inclusion in my LaTeX document. I want the pdf to be only as large as the circuit diagram, no larger. I don't want any unnecessary white space around the image.
So here's my cropping tip. Within Inkscape I select the circuit diagram I want to export. (I do the usual click-and-drag with the pointer tool to "select" all the elements of that one diagram.) Then, while selected, I choose the menu option File>DocumentProperties. The DocumentProperties window opens. There I click the button that says "Fit Page to Selection". That reduces the page to the size of that one diagram. (Don't worry, I don't lose the other 4 diagrams, because I don't overwrite the main .svg that contains the full set of 5.) Then I use Save As... to save the selection as a pdf by selecting "PDF via Cairo" from the list of output file types in the Save As popup window, and giving it a unique name. Voila. I have a pdf of my vector image painlessly cropped to the minimum size possible. No manual cropping.
At the Save As step I'm careful not to overwrite the main .svg file I'm working with. I still want to be able to go back and export the other 4 circuit diagrams as individual pdfs, and keep that .svg around in case I need to re-edit a diagram.
I certainly recommend keeping vector images in a vector format throughout the process. I do any scaling of the pdf image as an option when I call on the pdf from LaTeX; for example, \includegraphics[scale=0.6]{Circuit_1}. This seems to work flawlessly.
I'd be happy to read the details of others' image preparation workflow. It's a real bugaboo I've grappled with in various ways for a long time. Take care.