I got a letter almost exactly like that from Calloway Golf (makers of the Big Bertha Driver) because I had a porn site up on bigbertha.com
Nevermind that the term "Big Bertha" was originally used in WWII as the nickname for a large cannon..
But they had LOTS of lawyers on the list with addresses on 5th Avenue and I did not feel like fighting. Luckily I got the letter the day before I left for IA2000 and was able to talk to several domain experts and lawyers there and their advice was that unless I was making tons of meoney off the domain there was no reason to fight. I deleted the domain rather than give it to them like they asked. Someone else registered it right away and put up a golf site. I talked to him about a year later and he said that Calloway had talked to him and as long as he put up a disclaimer saying the site was not affiliated with them they would not bother him..go figure.. looking at the WHOIS now though it looks like Calloway finally got the domain although there is nothing on it..
One other cool domain thing.. I noticed seanconnery.com coming available a few years ago and used a script to grab it even though I had no idea what to do with it. After letting it sit for a year I put up a page stating that if Sean Connery wanted the domain I would give it to him for free. The offer was noticed by several people (the site usually got 500-1000 type-ins a day) and it was mentioned in several news stories. Sean Connery's agent eventually heard about it and contacted me about transferring the domain. After making sure he was not another crackpot claiming to be or represent Sir Sean (I usually got 2-3 of those a week) I arranged for the transfer. Still waiting on Network Solutions to stop dragging their ass on the transfer though. The agent went on Vacation in the Bahamas with Sean in August and had him give me a call and write me a nice letter thanking me for the domain. He also sent a cool autographed card with a caricature of him as Bond. Not bad for a $100 or so investment..
I also own charlesmanson.com

Thanks to California laws I can do whatever I want with the domain and he cannot do a single thing about it. Got a letter from him back in '98 not long after I got it. He asked me not to make him look like an evil person LOL.. A few of his "family" have also contacted me (at home which is weird since I have my old office # on the domain and my home number is unlisted) and I have never done anything actually about Manson on the site other than use his pic. I offer free e-mail on it and have about 15K users since late '98. Thinking of putting an Online Head Shop on it though.. Manson Bongs and Pipes and such

I sold Manson T-shirts a few years ago and sold out of my 200 shirt supply in about 2 weeks.. made about $10 off each shirt but the shipping was a pain in the ass..might do it again if I find a decent drop-shipper.
The point behind this long thread is that unless you are actually making money from a domain or have a purpose that cannot be achieved with a different domain name, why fight to keep it if you know you are infringing? All it will do is cost you money and time..and you will lose against someone with the money Gucci has. They are notorious for suing and winning claims against people for trademark infringement.