What's the best way to protect my furniture from tipsy guests who aren't careful about where they put down their cocktail glasses?
First of all, edit your friends. Second, don't serve red wine at a large party if you have white furniture. (Actually, I have tried this, but somehow they always manage to get hold of some and spill it anyway.) Third, treat your furniture with a protective spray to minimize the damage and have a professional cleaning crew on speed dial.
If the tabletop surface is glass, rings will just wipe away. If not, provide lots of coasters and napkins, and have a designated sober napkin changer (a.k.a. a waiter).
If you are entertaining family, pull out the linens and let them spill and stain away, then bundle them off to the dry cleaners (the linens, I mean). Another option is to clear away all your furniture and carpets and rent tables with tablecloths; that way, you can relax and even be your own tipsy, spilly guest.