Good point embee1.
Writing covered calls will generate some additional income above and beyond the dividends but probably not more than about one percentage point above the average dividends of the holdings.

One cannot argue with the quality of the stocks in the ETF but I am always suspicious when somehow one can turn the yield from a basket of blue chip conservative stocks into a yield of 7.4% - after an MER of 0.75%, so a pre-MER yield of a whopping 8.15% . 
To me a red flag (rather than a positive tax-wise) is that the dividends have been 100% ROC. ROC is not necessarily a bad thing (e.g. par for the course with REITs) but to get ROC from a basket of blue chip stocks is bizarre.

If one wants to garner 7% type yields - which I do (overall portfolio yield is 6.9% - RRSP 7.8%, non-reg 6.1%, TFSA 7.3%) I believe that one needs to hold a basket of individual stocks that pay out that sort of level - and, of course, one must have a relatively high risk tolerance.