I have played around with a lot of different interval ratios and found that 1:1 works best for me. I am a little faster doing that than 2:1 because I can run faster during the running segments. I can do a 12:00 mile on a good day, but tend to average about 12:30 on most of my long runs. Yes, it is annoying to keep starting and stopping every minute, but you get used to it.
I use a script that I downloaded to insert a "ding" every minute in my itunes playlist. That keeps me from looking at my watch. That program is here:
http://www.active.com/donate/tntntx/jeffwelch. I've taken a 170 beats per minute podcast and used a program called MP3 splitter (it's free for 30 days and I found it by googling MP3 splitter) to divide the podcast into 1 minute chunks. Then I used the script to insert the dings. It sounds complicated, but it isn't. PM me if you want me to walk you through it. Or, if enough of you would like the instructions I would be happy to post them here. I think most people just use a timer, but I can't hear them over my music and I don't want to drive the people around me crazy by beeping every minute.
Another useful tool is the run/walk pace calculator available here:
http://runwithperseverance.blogspot.com/. It allows you to type in your walking pace, your running pace, and your intervals to determine a time goal. It is fun to play with.