Sorry to object, but I think quoting any kind of vacancy rates (10%, 6 weeks a year, call it what you will) or maintenance costs ($300? Based on what?) is misleading and unfair.
In reality, there is absolutely no way to predict such expenses/income losses, and going off statistics for the area, similar sizes, previous deals or whatnot is a huge mistake.

The bottom line is – GOOD property managers will minimize your vacancy and expense. They will know their market, their areas, their tradies and their advertising packages, and will make sure they (and you) are on top of things IN YOUR PARTICULAR CASE.

Every property, area, month of the year, and tenant profile is a completely unique set of circumstances, and there's no room for guesses here. Think 10% and you'll miss out on a good agent that can make sure you lose less. Think 1% and you'll be miscalculating your deal and wondering what went wrong. In most cases, this can make for at least as much as your taxes, if you don't have a good accountant who knows what they're doing – why settle for less with property managers?

GET. GOOD. PROPERTY. MANAGERS. I can't emphasize that more. Whether you work through proxies or independently, this is your number one concern.

Brilliant thread, thanks for the great information – I'm also finding global real estate to be an exciting, profitable and great niche to be in. ))

Couldn't agree more with Alex – credibility, doing the right thing, knowing your stuff and presenting it clearly are the keys to successfull business, in this field and all others.