A couple of useful threads:
My thread about how I'm really enjoying GUMSHOE:
http://www.enworld.org/forum/general-rpg-discussion/316942-im-having-love-affair-gumshoe.html
A live play report for Night's Black Agents:
http://www.enworld.org/forum/genera...s-black-agents-tinker-tailor-vampire-die.html
Personally, I think Trail of Cthulhu is superb, and I think it's the best incarnation of the CoC rules. I like it much better than BRP Cthulhu or d20 Cthulhu.
The way Gumshoe works for General Skills (athletics, shooting, etc.), you roll one d6 and you try to hit a DC of (usually) 4. Before you roll you can spend points out of your skill pools. So if I'm shooting someone, I may spend 2 shooting points, then I add those to a d6. As long as I don't roll a 1 I probably hit.
For investigative skills, there's no roll required. If you have the skill, and you say you use it, you succeed - period. It's great. You can also spend those investigative skill points for bonus advantages. For instance, let's say my PC has Flirting as an interpersonal investigative skill. I flirt with the gorgeous but creepy swamp woman, and she tells me any clues she happens to know. If I want her to fall in love with me, and maybe betray her deep one father, I could spend a Flirting Point, but it's not necessary to learn clues.
The result is a fun, fast system that focuses on mystery solving instead of accidentally dying during standard easy rolls like in BRP.