speciesxx: check the section at the end of the
wiki article. galehar updated it, iirc, and i think it's still up to date. on boosts over 27, i think that was the original idea, but it doesn't seem to be implemented, as of a week ago at least (i know i hit the ceiling for stealth, which was getting boosted). you get feedback on the magnitude on the boost on the skill menu, so you'll know when to stop training.
on dpeg's:
but that usually happens later on. and if you're unlucky with scroll drops (which does happen) it may take a while to see his worth, unless you want to risk painting yourself into a corner wielding a lousy cursed dagger or somesuch. ashenzari is a pretty damn good (and fun) when he starts granting powers, but early on he doesn't help much, and forces a usually unproductive conduct (which you can ignore, at the cost of very slow piety gain, which again will delay the good stuff).
also note that the first poster's just starting out. the example on cursing gloves applies, and is something you can forget about. while it's more obvious, so does not being able to butcher with blunt weapons, or having to defer to animate skeleton, which pollutes everything with crappy allies which you may not want, and cannot be used on, say, insects (and which may just not be available). cursing rods is a no-go for all but the most experienced players. skill boosts are great but not-obvious, and unless it's changed, they are not well documented. there are many little surprises and you have to know what you're getting into. so ok, i use interface as an umbrella, but it's not just a conduct, in that things that the game makes easy for you cease to be so easy. my first games with ash were frankly a bit annoying. later on i made it to zot twice, and those were very enjoyable. that is my experience.