Depending on what you're building for, it can come in very handy. I built stalkers for around 30% or so in damage buffs and it definitely showed. In your standard PvE missions, you might not notice as much depending on your primary (EM vs Claws, for example), but against hard targets/PvP it's very nice to have.
"the reason there are so many sarcastic pvpers is we already had a better version of pvp taken away from us to appease bad players. Back then we chuckled at how bad players came here and whined. If we knew that was the actual voice devs would listen to instead of informed, educated players we probably would have been bigger dicks back then." -ConFlict
I've always dismissed the +Damage bonuses from sets as a borderline useless.
I built up a bit on my Sonic/Energy Defender and can't say I noticed much at all.
Playing around with my MA/SR stalker the other day I realised I could get a pretty decent boost (+25% or so) using 2 Mako's (4-slot), 2 Touch of Death, and 4-slotting my passives with Red Fortune (as well as 6 slotting the toggles), Adjusted Targetting in Focus Chi and Gaussian's in Tactics. All of which works pretty well towards building defence too.
I'll grab Assault on the way for an extra +10% Damage.
For a Stalker, this could have a very quantifiable difference, eg being able to one-hsot a taregt I couldn't otherwise.
Anyone had any good or bad experiences with this approach?