I used to co-run a public chat room on MSN--before it became a pay service. For any who used to frequent Pagan chat on MSN, it won't come as a suprise that love spell discussions were frequently brought into chat by newbies or trolls looking for a fight. It grew tiresome and we eventually developed the automated response for all the "Hi, I'm new to Wicca and want to learn how to do a love spell" people--manipulating the free will of another is wrong and will fall back negatively upon you. If you seek love in your life then "spells" can be done to invite it. If it was someone trying to bait us and cause dissent, I would simply suggest they carry a rose quartz, give a long and windy explanation on the properties of the stone and change the subject. It was entertaining for an over-worked host.
When faced with the subject now, after a long hiatus from the stresses of chat, I find myself still feeling the same. Do love spells work? I don't know. I've never done one. Why would they work? Because the will of the spellweaver was tightly focused and stronger than the will of the target person--same as any other spell involving an attack.
I believe that a love spell is an attack...the same as attempting to cord someone or tear the aura, infect the chakras or twist the inner sight. I don't follow a rede or believe in any "Law of Three". I do think that what comes around goes around. It may not happen in this life but eventually everything evens out. I also think that "instant karma", if it happens, is frequently a result of guilt.
All this said I think that love spells are wrong. I would never do one or reccomend another do one.
I admit that through my life, I have had my heart broken and experienced a level of loss and pain that most would describe as clinical and worthy or medication or "help". I've missed people so much that I truly layed in bed for weeks willing myself to die. I have been as black and broken as any human can be. I have never considered performing a love spell. I admit that my main reason for not doing so was not some lofty and humane goal of free-will. Rather, I wouldn't want love that wasn't freely given. It isn't real. I have learned since then and I know, more than ever now how important free will is. I know that there are Pagans out there who do thhese spells but I find them to be distasteful and reprehensible. If I can suffer at the hands of love as I have and not take that poisoned path then ther is no excuse for any one.
That's my opinion and it is not one that will be lightly changed.