I bought one way back in 2005, for music production. It lasted for about 4 years before it stopped turning on. at the time it was late 2009, which was middle of the recession and I couldn't afford to fix it. Shoot to late 2011, I opened it up to try to revive it (because I have 4 years worth of music production on it) and i see all the liquid cooling all over. I did some research, I find out that other people had this problem, so I called apple and complained about it being a health hazard and so on, and they told me to take it to a repair shop and they would take care of the repair, if it couldn't be repaired, they would send me a brand new one, (btw in 2005 I bought the computer directly from apple, so I think that helped), but the apple repair shop was able to replace with new parts, and its been working great ever since.
Also just recently found out about Logic Pro node, which allows distributed computing across a bunch of apple computers which allows me to keep my baby and purchase other macs to distribute the compute power, putting less strain on my 2.7
Meaning to reply to this earlier, but totally forgot. I found one by accident at a surplus by my local university. I had always wanted a mac tower, so my wife got it for me as an early birthday present. It wasn't until later did I found out it had a LCS. I have no idea how old it was but I got it back in June 2011 (this is the Quadcore 2.5Gb). Plus it was a surplus so I suspect it is probably at least 3-4 years old already.
It's working fine, mostly I use it for old games. I do have Matlab install on it, but I really can't justify running Matlab on it vs. running Matlab on my Mac mini (the power consumption).