I've never had a problem using normal oil, actually. The real problem is that people leave the oil in there for silly periods like 50K miles or more(if they change it at all that is). There's a bit difference between can last that long versus cheap and easy to change every year or two. Kind of like motor oil or antifreeze. You could get most oil to last 5-10K between changes, but it's so cheap that 3K or so is good preventative maintainence.
My rule of thumb is to use what the engine had in it originally, mostly because ancient gaskets and so on might not play well with synthetics. You never know until you change, but not changing is cheaper and you know it will still work.
