I do all my work in vectors. I do them at a high resolution and when I go from a vector program to a raster one I output to a lossless PNG file. Once I'm done with it I reduce it to a suitable size and output to a JPG with a decent quality to minimize artifacting for posting.
hmm never heard of using .SVG's before? I'll have to try it .
The way I always understood it, was that all Vector files must be converted into pixels before being able to be used on the net. PNG is good, but a high quality JPG file will do as well (smaller filesize). Save it at least at 72-300 ppi. 72 is good if you dont plan on stretching it out after saving as a JPG or whatever.