Mouse-Y axis seems to have diverted back to microscopic movement. Large moves only move the Y axis like two pixels up and down...

The y-mouse axis still works, (the ini setting)... However...

Whoever, "fixed it", seems to have broken it...

To get the same value as before, I had to adjust my settings from these settings... (In Skyrim.ini)
[Controls]
fMouseHeadingSensitivity=0.0360
bMouseAcceleration=0
fMouseHeadingYScale=0.0120
fMouseHeadingXScale=0.0110

to these settings...
[Controls]
fMouseHeadingSensitivity=0.0280
bMouseAcceleration=0
fMouseHeadingYScale=0.4800 <--- Note the MAJOR change. (Someone removed Mouse-Y/Game-Frame-Rate)
fMouseHeadingXScale=0.0120

I imagine someone ORIGINALLY had the formula as, (Mouse-delta-Y/Game-Time), now fixed with (Mouse-delta-Y/Game-Frame-Rate), however... your mouse does not need a delta, if comparing to frame-rate. (That is why the mouse was buggy, seeming to change WITH the frame-rate, as that is what delta would do... Not the raw Y value.)

Have you tried removing both values from your .ini file? Works for me.

I bet the original code just assumed the input would be constrained to whatever the console pad API provided them and applied some non-linear function, and then some genius fed it mouse deltas.

Yup... the Y-scale is broken, but in a different way for me.

Mouse sensitivity for the Y-scale is now HIGHER than the X-scale. For instance, when sprinting, try and move left-right with the mouse... it will go slow. Then try and move up-down with the mouse while sprinting... it will go very fast.

Regenerating .ini doesn't help.

Yes, you remove both, and now Y is not scaled to X correctly... Y moves too fast on wide-screen... Thus, the whole reason they created seporate X and Y values... I don;t need to look-up at mach-3, but I like to look fast behind me, and to the sides... like in real life. You can turn around faster than you can look up and down.

Removing the values simply locks X and Y scale to 1:1 ratio Which is perfect for a 4:3 (Standard screen or TV), but horrible for a 16:9 (Widescreen monitor)

Sprinting naturally reduces X motion. (That is a limit of sprinting, you can't turn fast.) Has not changed for me. It always limited my turning motion on sprint. You just have to move twice as far. It also reduces FOV to give the effect of running fast. (Might also be a loading helper, since it doesn't have to load as much perifial vision while sprinting.)

Oddly, walking slow... Which now seems slower than before... The game crashes more than when I sprint, and fly through zones without effort. (Eg, no delays loading things when sprinting, but walking freezes my computer for 2-8 seconds on every new object seen.)

The sprinting thing feels like a design choice, you aren't supposed to be able to turn on a dime when running fast, yet you can still move your head up and down without such limitations.

As for normal look, the y & x axis speeds now seem close to identical here. Before the patch when I had the scales set to the same values in the ini the vertical look was still slightly lower, and now with that stuff removed it's about as equal as can be. It feels faster because I'm not used to it in this game just yet but it's actually like a normal PC game now.