I hear most people are going for unholy dps now, using this spec.
But not long ago, when I had my naxx 25 man dps gear and 2x ghoulslicers (looks amazing dual wielding those), I was doing quite amazing dps for the gear (think my gearscore was at 4.200) and the DPS in a 5 man was at 3.8k overall, and in a 25 man toc I was doing 6K'ish on gormok.
keep in mind that most of my gear was naxx 25: 4/5 t 7.5, had a bracer iLevel 219 from toc, a chest iLevel 226 from ulduar, and the ghoulslicers. [I quit DPSing when ulduar came out, switched to tank] so yeah, imo it is very viable, I did also try the unholyspec, and for the gear I was wearing, DW dps was better with this spec, oh, and it is alot of fun. I am now blood DPS cause I got the bryntroll, which I also use for tanking atm, but I hardly go dps.