I extracted text geometry from postscript and then triangulated and deformed
that in userland

This rendered in about 10 seconds.

cylindertext.stl http://forum.openscad.org/file/t2140/cylindertext.stl

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"I don't think it is possible to know the horizontal extent of the text
string"

I just wrote a library that lets you get horizontal extents of text strings
for a number of common fonts: https://www.thingiverse.com/thing:3004457

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Another way is to use Hershey fonts where you have full userland access to
the lines. I wrote a quick library that does full uv mapping of text.
https://www.thingiverse.com/thing:3010934

To fit to a circle of radius 20, do:

mapHershey("Hello World!", f="let(angle=-u180/(PIr),r1=r+v)
[r1cos(angle),r1sin(angle),0]", size=10, extraParameters=[["r",20]])
cylinder(d=1,h=5);

(The cylinder() at the end is the profile of the virtual stylus with which
the text is drawn.)

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