Unfortunately there is no unified font handling system for Linux. You will have to configure each individual program so you can use TrueType, Type 1 or fonts that pique your fancy. And each program may well have its own way of doing this so you will have to RTFM. Desktop Environments like GNOME and KDE may provide much of this functionality however for apps that are under their control.
Most GUI apps should be able to use TrueType, and Type 1 fonts too. Wordperfect for Linux, however, cannot use TrueType. (See the links section below for more on Wordperfect.) Text editors, terminal programs and the like need fixed width fonts, and do not play well with TrueType or other proportional fonts (with some exceptions, eg gnome-terminal from GNOME-2, and xterm).
Though not discussed here, Type 1 fonts provide many of the same benefits as TrueType and are historically better supported in the Unix world, especially for printing. XFree86 still seems to render TrueType somewhat better than Type 1. You likely have many of these installed already. Unfortunately however, Type 1 are not a web standard like TrueType. But they are suitable for many other purposes. They are where it's at for printing. See ghostscript for more on this.
While it is possible to specify a default point size for the xfs font server, very few applications will actually use this value.
Abiword comes with a suite of fonts, called 'Abisuite'. Apparently, some of these fonts have the same names as some of the well known MS TrueType fonts: Arial, etc. And apparently, these are not as good quality. And because of the way X searches for fonts, it may find these first and use these, even if the 'real' ones are installed and may be the preferred choice. The solution is to either make sure your preferred fonts come first in the FontPath or maybe to uninstall 'Abisuite' if it's not needed.
The new Xft rendering extensions of XFree86 4.x will mostly supplant similar features as provided by xfs, and the older XFree86 "core" extensions. For instance, font aliasing should be set in XftConfig for Xft v1.x, and /etc/fonts/fonts.conf for Xft v2, if the new extensions are being used. This would only be true where the application is built against a toolkit (like QT or GTK) that supports the new extensions. This is still not universally supported.
XFree86 Project, the guys and gals who do an incredible amount of work to give us a killer GUI environment. An overview of XFree86 fonts: Fonts in XFree86. And an explanation of Xft: http://www.keithp.com/~keithp/render/Xft.tutorial.
The Fontconfig home page is http://fontconfig.org, for all the latest news on Xft and fontconfig (the future of X font handling).
The Video Timings HOWTO, the ins and outs of getting the most from your monitor. (Applicable only to XFree86 v.3.x for the most part.)
Font HOWTO Many good tips for installing fonts and for applications such as StarOffice, Applixware, Wordperfect, Ghostscript, TeX/LaTeX.
A TrueType HOWTO, good tips for printing, and a few application specific tips.
xfsft Homepage, TrueType font support for X. This is the origin of the "freetype" font module for XFree86 4.x, and Red Hat's xfs. Good site, and good links to other information related to fonts and TrueType.
Some Linux for Beginners. Great font site, and other Linux topics. Covers many of the topics discussed here in more detail. Some font and other tips for Mozilla: http://home.c2i.net/dark/My_Mozilla_FAQ.html.
X-TrueType Homepage, and yet another TrueType Font server, especially good for Japanese, Chinese and Korean character sets. [Note: link is bad 08/18/02.]
Tips on font size problems from Netscape.
Wordperfect for Linux -- Fonts and Printers by Rod Smith, the author of Using Corel Wordperfect 8 for Linux from Que. Excellent information on Wordperfect and where TrueType fits in.
http://sourceforge.net/projects/font-tool/, contains the core MS TrueTyep fonts suitable for web browsing. http://packages.debian.org/unstable/graphics/msttcorefonts.html is a similar package for Debian.
Sebastiano Vigna's http://gongolo.usr.dsi.unimi.it/~vigna/webFonts4Linux/ automates the downloading, extracting and installation of the Microsoft fonts all in one neat package.
Freeware Connection -- Free Fonts Sites lots of links to lots of sites.
Bitstream's Geometric Slabserif TrueType Font.
Two converters for converting a Mac Font "suitcase" to a *nix compatible font: http://www.macinsearch.com/infomac2/font/util/tt-converter-15.html and http://www.netmagic.net/~evan/shareware/#TTFontConvert
The Unicode HOWTO: http://tldp.org/HOWTO/Unicode-HOWTO.html
Two sources of 'free' TrueType fonts with large Unicode support are Bitstream Cyberbit, which covers Roman, Cyrillic, Greek, Hebrew, Arabic, combining diacritical marks, Chinese, Korean, Japanese, and more, and is available from ftp://ftp.netscape.com/pub/communicator/extras/fonts/windows/Cyberbit.ZIP. And Lucida Sans Unicode, which is included in IBM's JDK 1.3.0beta for Linux, and covers Roman, Cyrillic, Greek, Hebrew, combining diacritical marks. This can be downloaded from ftp://ftp.maths.tcd.ie/Linux/opt/IBMJava2-13/jre/lib/fonts/ as LucidaSansRegular.ttf and LucidaSansOblique.ttf. Thanks to Tzafrir Cohen for these references. He also has a nice page on Hebrew fonts and related topics at http://www.iglu.org.il/faq/?file=133.