Yes, they're poisonous. Use latex or nitrile gloves, or tongs to handle them. The wetwebmedia link quoted below says it all, and a good paper from JBC on the toxin.
From a good journal (JBC):
http
/www.jbc.org/cgi/reprint/258/13/7900.pdf
Other links:
http/www.wetwebmedia.com/ca/cav1i1/blane...s/zoanthids.htm
Quoting from above: Zoanthus and Palythoa both contain very toxic chemicals, that are dangerous to both reef inhabitants and humans. The most well known is Palytoxin, which has been documented as one of the most poisonous marine toxins known (Mereish et al, 1991). Palytoxin can affect the heart, muscles, and nerves leaving its victim in paralysis, and possibly death. Because of the toxin, you should never handle Zoanthus or Palythoa with open wounds, nor should you touch your mouth or eyes after handling the species. (Editors’ note: We recommend the use of disposable latex gloves) When propagating either of the species, it is critical to remember that the slightest rub of an itchy eye, or even a small cut from a hang nail, might be enough to land you in the hospital. In the aquarium, some rapid growing Zoanthus colonies can be aggressive to stony and soft corals, but in general, they are very peaceful, and you can slow the growth rate by the controlling the overall nutrient load of your tank.
http/www.wisegeek.com/what-is-zoanthid-coral.htm
Quoting from above: zoanthid coral are also equipped with poisonous toxins that can sting other creatures from the tips of their tentacles. This is solely for protection, not to paralyze animals for food.
http/www.geocities.com/CapeCanaveral/Han...eaking4_97.html
Quoting from above: Also be careful with Zoanthids, they are poisonous. Wash any of their mucous off if touched and don't accidently rub it in your eyes or they can swell up. Palythoa are used by islanders to make poison arrows.
i've touched the zoa's in my tank and i'm fine 
