When using the Font Hook, you cannot do special things on your own. For example, you cannot use your own drawing routines to speed things up. About a year and a half ago, I introduced an 8x8 font hook in BatLib and this is something I had never seen elsewhere. I had to do some semi-hacky things to display fonts in a custom way as opposed to just changing the data displayed and I figured this might be useful for others to use. Pretty much, if you want to use your own routine to display the font when the OS wants to draw a char, try adding this to the end of your hook:
   ld hl,18
    add hl,sp
    ld sp,hl
    pop hl
    ld a,l
    out (6),a
    pop hl
    pop ix
    pop hl
    pop de
    pop bc
    pop af
    ret
I am not sure if that works across all OSes, but I don't have access to them all The main scary part that could cause a crash is the fact that this readjusts the stack. If other OSes makes other calls or pushes/pops, this will likely cause a crash.

I used that to let me draw the fonts directly to the LCD and make sure the OS didn't try to mess that up. Plus, it skips over tons of OS code You will need to handle inverted text on your own, though, too. I just check the flag and use CPL on the data if it is supposed to be inverted.
Screenie:

As you can see, my actual hook needs help, too, because menus don't work, but the main part is that 8x8 fonts can work
EDIT: I have tested some OSes:
1.03 fail
1.10 fail
1.12 fail
1.13 good
1.14 good
1.15 good
1.17 good
1.18 good
1.19 good
2.30 good
2.40 good
2.41 good
2.43 good
2.53 works except in MathPrint, but doesn't crash
2.55 works except in MathPrint, but doesn't crash

I played with it for a bit before releasing that version, and one version did wrap text. The issue was that certain menus got really buggy.

When you set a font hook, it remains until you run a program that replaces it, disables it, or your RAM gets cleared

Well, if your font hook does, then yes (the example does use an archived font). The code is just a way to bypass a bunch of the OS stuff when it is returning from the hook

Well, I got an early birthday present from thepenguin77 so I have just now managed to confirm that it wil crash on OS1.03 and I still have to test others. It does work on 2.43 for sure since that is what i tested on before. I am right now working on a good fix, but to be universal will add a bunch of code

EDIT:(though that could be related to Bcalls)

Os 1.03? Do you mean bootcode 1.03? Someone should also test on the MP OSes, and whatever the current OS for the old TI-83+s is. (1.16?)

I don't think OS 1.03 matters much, considering it cannot run apps, apparently, or can barely run any. As long as it works on OS 1.19, 2.43, 2.53 and 2.55MP I guess it's fine.

I think it only came on very few calcs too. Most calcs in the early 83+ days had OS 1.12 I think.