What fonts do you use? The first thing I do when I set up windows is change the default font to Verdana. I even have a reg key which does this for Win Office, saving me the hassle of clicking through numerous dialogs. I really dislike Arial and Times New Roman. However, I've been thinking of giving Georgia a spin. Unfortunatley, Arial is the default font used in Outlook and Excel and I have to deal with looking at it all day long. The majority of e-mail I see at Microsoft is written using Verdana. So a lot of people must like it enough to go out of their way to change it.
Some folks are very particular about the fonts they use. I find that Verdana and Tahoma are the most readable Web/Email fonts and I use them for everything. Arial looks to skinny and horrible on a Macintosh. Tahoma, Verdana and Georgia were designed by the renowned Mathew Carter. In addition you'll find that Pocket PC and Smartphone have a font called Nina which looks fantastic and tiny font sizes (like 7).
For an interesting article, check out Nina, Verdana and Tahoma compared.
And if you are using Windows and have an LCD you'd be crazy to not have ClearType enabled. ClearType is probably my favorite Windows technology. If you have it on you'll want to run the ClearType tuner.
Finally, if you write code you'll want to check out ProFont which blows Courier New out of the water. I use the TrueType version (which gets ClearType support) rather than the bitmap version. It looks great at 8pt and is about 20% more compact than Courier New.