That depends on whether it has been seamed or has edgework. It's incredibly sharp if nothing has been done to it, enough so that merely touching glass edges can cause cuts. Glass is normally seamed before tempering, but that doesn't leave it perfectly smooth either. I've gotten glass splinters from it, along with finding edges that didn't get seamed well, though most sharp edges will break in the tempering furnace (this is why you seam glass prior to tempering). Glass splinters are as horrible as you might imagine and can take weeks to work themselves out, as well as being ridiculously hard to see.

So yeah, I don't recommend the practice if you're not sure, but it may be okay for glass that has had edgework done as this glass gets polished smooth, whereas tempered glass is probably okay, but not always safe.

EDIT: Looks like it's blown glass. No, that's not very safe.