I've only burnt one bluray to date, since I purchased my laptop with a burner built in.
Aside from being a laptop, the speed of bluray isn't at a stage where I find it competitive. It may add an extra layer of redundancy to your data, but personally, the time spent burning a bluray, is better spent uploading it to a portable hard drive unit.
I can't say I've written more then once on a single disk, but from personal experience, like the others, it's been problematic doing so on DVD's from day one... and continues to this day.
The benifits of DVD's is that they're pretty cheap now per disk, and if you don't fill one up, it's no great loss.