cluckhead
It's definitely not easy to make money; my experience is much the same as birchy's inasmuch as the margins I achieve are laughably small - couple of hundred grand a year stakes to make a thousand pounds or so - nowhere near minimum wage when you consider the work involved. Even then I have the odd losing month, so giving up the day job isn't an option (yet ).
If you couple this with the fact that betting exchange markets are still evolving, so a method that was profitable a year ago may well be a loser today, you will see that this is just a hobby for most of us, although if you are bright and work hard at it the main cost will be time rather than hard cash.
There are two ways to make a living from botting - (1) buy shares in betfair (2) do what gruss and stefan do, write the easy bits, put them in a slick package and sell them on - my two bob on the current flame war is that these are valid products, but using this forum to plug them is out of order. It's a DIY forum, after all - If stefan wants to contribute for the fun of it, I'm sure he could offer a lot of constructive advice; unfortunately most of his posts to date are just adverts for his framework.
denp
You are dead right, mate. I think you can classify 'systems' into two broad groups; trading (or market making) and punting (where you take a view on the 'true' price and bet to that). I'm a punter myself, because that is the challenge that captured my imagination thirty-odd years ago. As you say, punting isn't that time-critical, but cluckhead's original post talked about "buy low sell hi etc", which I assume makes him a trader - hence my low latency advice.