While I haven't picked up GT yet -- it sounds like something I'll like, but it's not what I need for the current campaign -- I wanted to chime in a bit about Skill Use in 3.x and d20 Modern and such.
I think that the "power creep" factor is certainly a point, but I also think that it's something that can often be worked out with good communication between players and GMs. This was something I brought up with my players at the start of a campaign awhile back. Here's a paraphrase of what I wrote:
"Okay, after looking around at the system, I've decided that for our campaign, an Average, Retryable, Non-Critical skill check will be about DC14+(your level). Since you guys are starting at 6th level, this means that a skill check I consider "not too hard" and "not too easy" will be DC 20. If it's critical to your advancement in the story and/or not retryable, it's probably going to be easier, or there will be factors that you can most likely use to get bonuses on the check.
So, generally speaking, think of yourselves as shooting for DC 20 on an average check. Here's what that means:
A character with max'd ranks in a class skill and an ability modifier of +2 will have a +11 on his check (9 ranks, +2 ability). This means that he succeeds on a 9 or higher -- he has a 60% chance of success. In this game, that means he's pretty good at that. This is something he is competent and noticeably adept at.
A character who adds additional stuff, like feats and/or class abilities, can get that up significantly higher. For example, a PC with three levels of Dedicated could take Skill Emphasis:Sense Motive and Empathy. Together, those add a +6 to the check, meaning that our PC now checks at +17 -- an 85% chance of success on the first attempt of an average, non-critical skill check. This person is a specialist, somebody who can get it done even if it's extremely difficult. This person is focused -- they're almost always going to succeed, but they're not as flexible.
A character who has put a few cross-class ranks into this skill, or taken a feat without taking ranks, might have a check of +6 total, including ability scores, feats, cross-class ranks, and so on. This means that he needs a 14 or higher to hit the average roll -- a 35% success rate on an average check. This character can do what's being asked of him, but it's going to take him a bit longer. He might take 12 or 18 seconds (2-3 rounds) instead of 6 seconds to get something done, but he still gets it done.
So, to sum up -- at your level:
Check at +0 or worse: You are noticeably bad at this, and probably shouldn't try to do it if other people are around who can do it better.
Check at +1 to +5: You probably have some training or natural skill in this area. Nobody is going to mistake you for an expert, and this is definitely not your strongest suit, but you can do it competently and won't need help to accomplish ordinary tasks.
Check at +6 to +10: You are recognizeably skilled at this type of thing, and can, with time, accomplish things that other folks would find completely impossible. If you have time to move carefully, you can do some truly impressive stuff, and it probably only takes you 2 or 3 tries on something that's meant to be an average challenge for the party.
Check at +11 to +15: This is an area of focused expertise for you. You can do challenging tasks on the first try, and you can do some very very difficult tasks without looking around for ways to make your tasks easier. If you have time to move slowly and carefully, you can pretty much assume that you're going to succeed at just about anything in this area -- and if this is a non-retryable skill, you have enough ability here to confidently use this even in situations when failure would be BAD.
Check at +16 or higher: You are one of the best people in the world at your level of experience with respect to this skill. The game should never require a skill check this high to proceed. Skill at this level means either that you want to succeed pretty much all the time on the first try, or that you want to be able to cut corners and succeed on stuff without finding other ways to get things done.
So, with that information in mind, build the characters you want."
That's about what I told them, anyway. I did receive a couple of complaints from people who thought that the skill system was lame, and that they should get more skills, so that they could have all of their skills max'd out instead of putting some ranks into everything they wanted to be good at -- resulting in them being good, but not superb, at a lot of things. When I talked about it with them, it kinda came out that they really wanted to be superb at a lot of things... which, they admitted, really meant that they wanted to be a higher-level character.
In my (limited) experience, problems with 3.x skills and skill checks usually boil down to:
-Players wanting their characters to be max'd out in too many areas, instead of good in many areas but not max'd out.
-GMs reinforcing this behavior by making skill check DCs so high that only characters with max'd out ranks have any chance to make them.