As Conorh said, if you're going to do a split, micro-periodization has been shown (and I've experienced it firsthand) to be much more effective than linear periodization. I.e., say you're hitting each bodypart twice per week. Have the first time be a heavier, lower rep day and the second time that week be a higher rep day. When doing a split, I would aim for failure on every set.
If you've got the time and recovery ability (i.e. if you can almost dedicate your life to it!), I've found a 6-day per week schedule, where you hit each bodypart 3 times per week, with low rep, medium rep and higher rep days for each bodypart each week, to be ideal. (And yes, I'm talking about natural training). That's probably not feasible for most people, though.
The first time I switched to a total body scheme I was surprised that I actually did make some progress -- I was convinced that I would at best just maintain, and probably even lose some. However, I can't say that the progress was at quite the same rate as doing a good split routine. I just find that the splite routine requires more time (workouts per week) and recovery ability (got to be getting enough sleep, eating and supplementing right, etc.).
Just my .02.