I had 5870 Crossfire. I was running 3 monitors. The performance wasn't there for what I was trying to do at the time.
When I heard nVidia was introducing Surround, I switched over to GTX480 SLI. I couldn't have been happier with the performance. However, I would constantly get this strange issue where the driver would crash at the desktop during normal non 3D use. I tried everything to figure out the issue, but never could. Despite that, I tolerated it as I mostly used my machine for gaming. Also, Surround gaming wasn't quite as well implemented as was Eyefinity. But it was good enough and got me through some good games with a good gaming experience.
When the GTX580s came out I thought it would be a good idea to upgrade. I thought better performance with less heat and noise and the potential to solve my driver crashing issue would make it worth it. My cards were from eVGA and I had hoped to use their upgrade service. Unfortunately I was 2 days past the 90 days and eVGA wouldn't budge. So I was forced to sell my GTX480s on ebay and buy the GTX580s. In all my video card purchases and sales, I had never taken such a loss in selling cards back. The only other nVidia card I had ever owned was a 6800GT, which I was able to sell for more money than I bought new over a year later (actually I did own one other, a 8800GT and was satisfied with that card). So imagine my surprise when the GTX480s sold for less than 50% of what I paid for and they were less than 4 months old.
Regardless, I had my GTX580 SLI and the performance was good. Unfortunately outside of gaming again, I continued to have issues. My machine was having the same crash issues as with the prior cards, only more frequently. I was becoming frustrating. Instead of gaming, I spent most of my time troubleshooting and throwing needless money at the problem trying to solve the issue. Most of the time I only had a single GTX580 in at any given time trying to recreate the issue to determine if one card was bad. After a long period I began to suspect one of my cards was bad and decided to RMA the card to eVGA. I had heard only good things about them and was expecting a smooth transition. Boy was I wrong. I'm not going to go into the details of why the experience was so bad, but I'll just let you know that I won't be buying any more eVGA products in the future. Thankfully if I ever return to nVidia, there are other options.
Of course after getting back my new (wasn't actually new, was a refurb card) card, the issues still plagued me. I had had enough and just wanted to rid myself of the constant dealing with issues. So I once again, decided to sell the GTX580s in favor of something else. Again, the cards were fairly new, and still I took a huge loss.
So in a years time I lost a lot of money due to the cards quickly depreciating in value. My user experience was mixed in that the gaming was pretty good and showed good performance. Also, I made use of CUDA for a lot of video encoding projects I had going on. So not all was bad. But the negative left a bad taste in my mouth. I was ready to try the only other alternative.
So I opted to go back to AMD and try the 6970 Crossfire. I knew I'd be taking a performance hit, but I was worried more that everything just worked by that point. And I must say that it did. My user experience with those cards was nothing but positive. No crashes and performance was still good enough to keep my happy. I still couldn't always have the performance I wanted in Eyefinity, but at least single screen let me turn on all the eye candy I wanted. The only caveat was of course the well known issues with drivers not being ready on game releases. That didn't make me happy, but it always did get resolved to my needs in time.
So while it's being hinted here that Kepler will probably be quicker than 7970, and I believe it probably will, I'm not sure it matters to me. I'm only looking for the better user experience, and I only need so much. I have two 7970s currently in Crossfire and the performance is great. The drivers have already soured my user experience however. But I'm hoping again that in time those issues will resolve and I'll largely forget my initial impressions with the drivers. An if the drivers become as good as they were with the 6970s, I'm not going to feel regret for not waiting for Kepler, no matter how much faster it is (easy to say when you don't yet know