I have had mixed success bottling with molasses and maple syrup.
I've made two different brown ales and I bottled both using molasses as the priming sugar. A slight amount of the molasses flavor came through, which I really liked.
I made a maple syrup porter that I bottled with maple syrup. Again, a slight hint of the flavor was noticeable in the finished brew.
The "mixed success" part had to do with the aging. None of the three beers had a very good shelf life. All tasted great initially, but changed dramatically as time passed. I had the biggest problem with the maple syrup porter. It tasted great for about the first month. By the second month, the beer was on it's way to cloyingly sweet. By the third month, it was undrinkable.
The brown ales had a slightly better shelf life, but even they changed over time and the final bottles did not taste nearly as good as the initial ones.
None of my other beers (bottled with DME) have had this problem. In fact, almost every brew I have gets better with age. I used DME to bottle my third brown ale recipe and the remaining bottles are still delicious after 6 months. Only the ones I've bottled with maple syrup or molasses had shelf life issues.
Great taste to begin with, but drink the batch fast. That's my experience. YMMV.
Scott