Not bad...but with a little leverage you can do better than that in munis.
For example, BSD is yielding 6.51%, which is about 10.02% tax adjusted. Or if you have the privilege of paying 46% of your income to the tax man because you live in NYC, BNY yields 5.65% or 9.71% tax adjusted.
Although these yields aren't spectacular compared with what you can get elsewhere, they're pretty damn good, plus you get the satisfaction of not paying tax. Unless, of course, you accidentally get hit with the AMT.