Plax, I've been in exactly this situation. For whatever reason, I don't use a bike any more and found that I was getitng steadily more and more unfit. I started running mostly to encourage my brother (who was even less fit than me) and have now got really into it. The reason I like it is that I can go for a run if I've got an hour spare: cycling always seemed to take up the best part of half a day, and I'd certainly never get around to going in the week.
Ignore those who say that the toys won't get you out of the door ... they do! I go out running to gather data and try and beat my records as much as just for the fun of running. I bought myself a Garmin Forerunner 10, having read about issues with the waterproofing of the Forerunner 110, and so far as I can tell, the FR10 is the better tool. Dead simple to use and very robust. I was so impressed that I bought my fiancee one as well. Well, actually I was more annoyed that she kept pinching mine.
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Good luck with it. I'm so hooked that I've started doing 10K races, and am training for my first half marathon in nearly 30 years. I'm even planning to run a 10k for my stag do, probably wearing a wedding dress if my best man's got anything to do with it!
If you do get a Garmin, you can send me a friend request on Garmin Connect if you like, I'm Rhythm Thief on there too and can be found at
http://connect.garmin.com/profile/RhythmThief . I'm only connected to my brother and my fiancee on there, but I find it really encouraging to get comments on my running.