Personal experience says yes it does - although initially the combination of the different muscles and the impact/weight bearing nature of running is counter productive. This goes after a few weeks at the most - sooner if you stretch more - as your legs adapt to the combination of the two forms of exercise.
A few years ago I did a season of duathlon racing - which by definition involves both running and cycling during the racing season. I know that the biking in this is different to bike racing, but I was still doing a few bike races over this time and it seemed to be OK. During this time, from memory, I averaged about 350km riding and about 30-50km running per week - the lower running reflecting that I come from a biking rather than running background.
More recently, I spent the early part of this season doing (pretty serious/gnarly) trail running a couple of times a week - having come off a winter of XC skiing - and found that the impact on my cardio vascular performance was huge. It also helped me build a certain toughness into the legs - hard to describe other than to say it was like a fast track to some race fitness. And like David Suro says, it helps core strength well and truly.
For me as well, I find that my body responds to throwing in one or two cross training sessions throughout the season - which are running and yoga.
I also put in about six solid weeks of running every day in mid summer - prep-ing for the cross season. It wasn't anything long - only around the 20min/5km mark - and was a combination of road and off-road/city park running. This gave me another leap on in general cycling fitness - again, to me it feels like that "toughening up the legs" thing ... Didn't seem to adversely affect my riding - but it did mean that I had to be more particular about stretching every day to ensure that I stayed flexible.
I'm sure that the benefits go both ways, as I know that my running speed improved out of sight for the amount of time that I spent running - and I've had one of the best summers on the bike for ages.
I know that there will be a number of other posters who will disagree - after all, standard logic in the cycling community is that you can't run and that it'll stuff you up completely. As I say, my experience is that this old school position is crap for anyone other than a really serious rider putting in major k's per week. But under those circumstances, your muscles will have become so specialised that anything other than biking is going to be counterproductive.
As with anything though, it depends on the person concerned - so try it out for yourself, see what works for you. Most of all - have fun with whatever your training is!