Do a search, it has been discussed.
pro: lightweight, cheaper (initially- .17c a foot, but need to be replaced more often), doesn't cut you. If they are spliced they are stronger than the steel wire.
con: have to keep a close eye on them and replace them once wear shows.

I did a set for my previous boat and they worked very well. We replaced them mainly because it is difficult to find a way to really limit the friction/abrasion where the line attaches to the hounds. We also used 7/64 amsteel which gives you less room for wear. But then again, a 230lb dude on them probably causes more wear than average. I did them on another HT and they are working fine.
They should be replaced yearly at least though IMO (differing opinions, etc). If you don't pay attention to them and have no intention of paying attention then certainly stay with the wire.
I was a little hesitant to do it on my boat because I singlehand so often. However, I did do it and it has worked fine. I am fairly OCD about going over my boat routinely though.