Okay, so I didn't get past the finals of the UK rising stars of manga. Still, getting to the finals first try is nothing to be sneezed at! My entry, 'Fell' made a fair number of people laugh and showed that having regional dialect English doesn't harm your chances as people had previously believed.
I'll be entering again next year, and I think you should too (assuming you're a manga artist from the UK or Ireland, though if you're American, obviously, you could enter the big rsom). Reasons to enter the uk and ireland rising stars of manga:
1. Not bad odds. Okay, so most years there will be about 250 entries from around Britain. This year there were 16 finalists and every year there are 7 or 8 winning places. You're way more likely to win the rsom than the lottery!
2. Experience. I learned a heck of a lot by doing an entry. I learned about time management, how to ink with a nib pen, how to use screentones, how to work to technical specifications and all about bleed. Even after I was done, I learned from mistakes I'd made about left and right pages and stuff!
3. Community. The British manga community is a small one and it's very supportive. Join the group 'UK manga ka' here on TP or become a poster on the sweatdrop studios forums at http://www.sweatdrop.com and you'll have access to advice and criticism from many of the previous uk rsom winners and finalists and lots of experienced hobbyists and professional artists. You'll probably end up friends with your fellow entrants, making it hard to hold a grudge if you don't get in the finals or the book!
4. The publicity. Finalists go on the website, winners go in the book. Even if you don't get in, you can put your entry online as a webcomic, or print it and sell it at a convention. Finishing an entry, even if it doesn't get in, still leaves you with a fully completed doujinshi, something which shows you can finish what you start, shows off your skills and demands respect!

So, when the uk rsom 4 is announced, I hope you'll be joining in! Put aside a month or two for drawing and printing and panicking this summer!