In the kitchen, no. In the living room, yes, I use my Cambridge Audio Dacmagic.
Yes, in my opinion DACs do make a significant difference to the sound. I could plug my Connect direct into my Onkyo AV receiver via an optical cable (i.e. using the DAC in my receiver) in the living room, but I personally think the Cambridge Audio improves the sound of the music when I've done back to back listening of the two.
The kitchen setup is compromised massively (speakers sit on top of cupboards) and is really just intended to allow internet radio / music in the kitchen - as such, I'm not too bothered about improving the quality of the music in there.
I should point out, I bought the Cambridge Audio a while back for a completely different purpose - at the time I didn't really do any auditioning between different products - I just needed a solution to a problem and the Dacmagic fixed that instantly with a good deal from my local Richer Sounds branch.