HI - been lurking in the shadows for a month or so, but this is my first post
I've been mining for two weeks on a couple of CPU's and a laptop GPU but was only collecting about 0.02btc per day (maxing out at 7 mhash/sec).
My old 2006 Mac Pro really needed a bit of an upgrade so amongst a few other bits I found a XFX HD5870 for £120 (UK).
Tested that on and off for a day or two, but was disappointed to only get about 114 mhash/sec in OS X. Since then have discovered that Apples open CL implementation isn't the most efficient out there.
I've now installed Ubunutu on a partition, and overclocked / underclocked the 5870 to core 950 Mhz / Memory 300 Mhz.
I use Phoenix with the phatk kernal and now pull in a respectable and stable 420 Mhash/sec at 75ºC.
I've been running with that setup for around 24hrs now and mined just under 1BTC on Slush's pool. I think this will drop dramatically in a day or two when the difficulty rises... although I still don't really understand what drives that.
I'm sceptical by nature and to be honest I really don't know how bitcoins will go in the future, especially after the past few days, but one can hope. My main target at the moment is to cover the cost of GPU and electricity whilst slowing padding out my wallet with a few BTCs.
So far I've really enjoyed the learning process and tinkering to get to where I am.
I now know a little about bitcoin, overclocking, and Linux where previously I knew zilch, so for me its already worth it. Plus my Mac has a shiny new upgrade and is now a semi decent graphics machine too (I spend half my day in photoshop, so the GPU really helps)