I suppose that would depend on which magazine you are advertising in. If you are putting an ad in Home & Garden magazine, I highly doubt anyone will buy your music or even pay attention to the ad (well maybe they would look at it and think 'why is this ad in this magazine?'). If you are placing the ad in a music magazine that is specifically targeted towards people who are purchasing electronic music - whether it be djs, or just clubbers who like to purchase music for their listening pleasure - then I would imagine these are the kinds of readers who would be looking at your ad. Generally, when you are placing an ad in a magazine, you want to find out a couple of things from them - like how many people subscribe, what territories do they circulate to, how many people read the magazine - things of this nature. Then based on those numbers, decide if it's worth spending the money for an ad. Also take into account that a smaller label, with a smaller budget, obviously wont be paying as much money as what bigger labels do - so it might not be a bad idea to place an ad if the magazine is willing to give you a good rate. Does that help answer your question or was there something else you were curious about?
Other avenues of promoting digital releases - myspace - you now can have a beatport player on your page with a list of your releases and the opportunity for people to buy, which I think is a useful tool. The downside to myspace though, is that I see too much spam coming thru my in-box telling me to listen to people's tunes and buy their music. But, for every one person like me who hates spam, there's always one person who actually will be inclined to listen to and possibly buy the music when they get such emails on there.....