I've never heard anything negative about them but have never known anyone outside of the engraving side of the business that used them. Although I understand they now include vinyl cutting files in their offerings, they are primarily known for their logo digitizing services ... which I gather is the primary source for their library.
I'm a bit put off by the fact that they don't allow online browsing of their images. I gather that comes after you sign up for a subscription ... unless I am missing the link somewhere. But for $9.95 for a month, you really don't have much to lose.
If you're looking for other online sources, please look over my two clipart sites:
allcompu.com for CD collections with books
expresslipart.com for individual images for immediate download.