(I searched a bit but didn't find any discussion on this, so please forgive me if I didn't find some old thread that explains this.)
I am (like many other Glitchlings) now at 101+1 skills. I have a Capacity of 40, which essentially means I'm at 62 over capacity, with a 1959% time penalty. According to the "About Brain Capacity" info popup, the penalty grows by five percent for each skill, and the examples show 32/30 (10% penalty) and 29+1/30 (5% penalty). Maybe because of how low these examples are, it seems that these are linear addition of 5% of base time, but based on my time penalty it seems that we are given an exponential penalty. Sort of.
101+1/40, or 102/4, if we were given a linear growth, would be a penalty of 310%.[1] Exponential growth would be some 2059.38% penalty[2]; at 101/40, it's 1961.3%, which is only 2% different than the penalty I actually have.
To be clear, I don't object to the long time it takes to learn these advanced skills (and in fact like the use of exponential growth in other places, such as Upgrades), but the info popup does seem misleading.
[1]. 62 * 5% = 310%
[2]. 100 * (1 + 0.05)^62 = 2059.38