Tommo - For your sake, I hope GKP don't go the same way as XEL - I could have sold at a massive profit, but I now sit on a pretty big loss as I didn't sell. I'm afraid I don't know much about GKP so I don't know if it might!
I've only been investing for a short time too, and have mainly been O+G. I've made a loss on DES, XEL and EO. I could have sold all of them at a profit, but didn't do it in time, because I told myself I was investing for the future. Luckily I did very well in NPE, and was much more sensible top slicing a number of times, and still hold more (in value) than my initial investment even though I've sold pretty much all of them. I made a very small profit on RKH, but I don't feel Falklands is a good investment at the moment, just a gut feeling (maybe influenced by the DES sting!).
Just remember that profit is profit, and when you are up massively as you probably are with GKP, then it can be a very sensible decision to reduce your holding and diversify, or just hold the cash in anticipation - there have been a lot of opportunities this year that I've missed out on because I don't have any cash.
Right now I'm dealing with small amounts, and playing it quite risky. My great grandmother always used to tell me "Only buy shares with pocket money", but when I do make decisions, I try to think to myself - what would I do if there was another 0 or two on the end of this number - would I still buy,hold or sell?
Anyway, there isn't much wisdom to my ramblings, just a warning that by "Investing" rather than "Trading" since November 2010 which was the highest point of my portfolio, I've seen the value of it decrease over 50% and it's pretty much worth the same as I've put into it. I'm certain much more experienced people on here will wave their arms saying "we told you so!" - and they did, but I made my own decisions and got them wrong - but it's all a learning experience for the future!
Good luck - "may the odds be ever in your favour"