I've been using linuxcoin and the poclbm miner, because I'm not familiar with linux, or X... LC is still a work in progress though because the default settings do not maximise the throughput. Today I read up on the options and adjusted a couple of the commandline args and managed to leap from 250 to 299 Mhash/sec on my 6870, which is a massive difference.
this thread also describes a simple optimisation which added a couple more Mhash.
Similar commandline option tweaks on the winbox got the 5570 past 72Mhash/sec, but before that I was running it for nearly 3 weeks with the defaults on the Linux box only getting to 61Mhash/sec...
The realisation that I was 20% down for 3 weeks is made worse by knowing I'm getting into this too late. According to
http://bitminer.info/, at the moment the cost of electricity versus income with a 5570 is now about 50%, with a projected break-even of 106 days. A couple of weeks ago it was <20% and 29 days to break even. The 6870 fares a little better, but it's still trending downwards as the difficulty increases. At some point in the near future the cost of electricity will exceed the value of the coins it's creating. I'll hit that limit sooner because I pay a bit more, but others won't be that far behind. I wonder what will happen then? Will the value of BTC increase as they become more rare?