I've been reading this thread with interest and there seems plenty of good and well intentioned advice on it.
The problem I have is this overwhelming sense of having missed most of an opportunity to be quite good at something. I don't know if anyone else can relate to this but i've always been pretty decent at sports but never really taken a single one seriously enough to progress in it. Now I have scaled down to just running and golf as these are both sports that I can continue to do into my old age, so it made sense to get focussed on them.
If I can be self-indulgent for a moment and explain my background. I've been running casually for about 4 years. First 9 months with untold pains, last 3 years or so with none whatsoever (thank God). I ran 98% 5k runs up until about 5 months ago and then started doing the odd 10k, probably 10-15 (I never kept track) in total. I'd run 3-4 times a week with a weekly mileage of 9-15 miles per week. Not much. Here's the thing though, I entered the Salford 10k a few weeks ago and finished joint 99th in a time of 41.46. This, despite not realising where I was supposed to start and there being over 2 minutes difference between gun and chip times (first mile over 8 mins because of battling through the throngs) and then falling over my own clumsy feet with 2k to go and hitting the deck - ouch! Since then, i've done a training run of around a 40 minute 10k, on hills. Did my first park run in Bolton last week, 19.30 on a hilly course.
I do believe that my times, off the back of little formal training and only a handful of runs longer than 5k, show promise. I suspect I might have potential to be a half-decent runner and i'd like to capitalise on that. I've now started to realise that my training was a farce. All I ever did was go out and run and tried to beat my own PB every time. With that and my low weekly mileage, does that make those finish times more surprising? Perhaps they're not as good as I think they seem.
Damn, i'm prattling here. Sorry. The point i'm trying to get to is that i'm frustrated with myself. I'm 34 now and should have started all this 10 years or so ago. I don't rightly know how much longer I can continue to improve before ageing starts to counter-balance the improvement. I'm in a hurry now. I want to see where I can take this before it's too late and that includes scaling up to marathons and maybe even ultras after that (depends if I enjoy the marathons I guess!). Since the change of mindset I have run 12 miles (last Sunday) in about 1.28 without really pushing it. I will scale up to longer runs as time goes on but I also don't want to push too hard too soon.
So I appreciate all the sound advice on here about scaling up slowly and perhaps trying to settle on one race distance that suits you best but time is not on my side, unfortunately. I want to find out what i'm really capable of and that has to involve scaling up the mileage. I'd really appreciate some person/scenario specific advice that could be applied here 
Edited: 19/09/2012 at 09:41