I too was involved in a long distance relationship, which lasted for 3 years. We met online on a BtVS femslash group on Yahoo, I left quirky feedback for a few of her fics, and she thought I was funny. Then she met Amber Benson at the premiere of 'Chance', and all her friends were sick of hearing about it - so she e-mailed me. Thus started a firm friendship, and hardly a day went by that we didn't e-mail or IM each other.
That was in September '02. By November we were flirting constantly... I think we both realised our feelings had deepened, but we were both too scared to say anything. Then in January '03 - the 18th, to be exact - the city I live in was hit by a once-in-a-century firestorm. Not just a bushfire... this thing was fuelled by raging winds, and burned through a national park for a week before it got near us... then in the space of 2 hours it took out over 400 homes. At various points over the next 4 days my home, my brother's home and my parents' home were all under direct threat (I remember spending the afternoon of Tuesday the 21st sitting in my backyard, stamping out any embers that the wind carried over the fence).
That was obviously the kick up the bum that we both needed to push us into action, cause 3 days later we finally admitted how we felt to each other during a very emotional phone call. Visits were few and far between, as she's in the U.S. and I'm in Australia - we spent three weeks together in May '03 (she flew over here), and then another three weeks over Christmas/New Year (I flew over there)... then last year she got a long-stay holiday visa, and stayed here with me for 6 fabulous months.
Sadly, what became apparent over that 6 months was that my feelings had changed (I worked out that while I love her dearly, I'm not
in love with her any more), and we broke up in January this year. We had a lot of ups and downs over those three years, and a
lot of emotional baggage to deal with, which (combined with the distance and time difference) made things very difficult at times - but I am happy to say that she is still my best friend, we still have regular contact (though not every day now, as she's driving trucks for a living and often can't access e-mail), and we can still talk to each other for hours on end about anything and everything. And I still have to send her 'care packages' - filled with all the things she got hooked on while she was here that she can't get in the States (she still wants me to work out a viable way to send her meat pies and kebabs!).

Over that 3 years, we did talk a lot about the possibility of one of us relocating to live with the other (most likely she would have moved over here), and the one thing we always agreed was that in the first instance, whoever relocated shouldn't break all their ties with home. The bottom line, as I'm sure you'll agree, is that being with someone in person permanently is very different to being with them for a short visit, and worlds away from speaking with them online or on the phone. We were always careful to prioritise our friendship, and promised each other that if we didn't feel the same way after spending a good amount of time (i.e. 6 months) together in person as we did online, then we wouldn't drag it out... we'd walk away from the relationship, and try to preserve our friendship, which we both treasure - and I'm glad we did, because she's still one of the most important people in my life.
So the only suggestions I would offer (over and above those already made by other kittens): Leave some belongings (furniture, car, etc) in storage or with family/friends rather than selling them all, and definitely rent out your house rather than selling it immediately. Give yourself options: something to go back to, just in case things don't work out the way you planned - or a 'nest egg' of assets that will assist you in making your permanent move, if things
do work out. Hope for the best, prepare for the worst.
I wholeheartedly agree with what nearly everyone has stated here - you
can make a long distance relationship work. It's not easy, and can be downright painful and agonising... but it can be
so worth it.

[/long-winded, drama-filled ramble]
mudrat