Gah, so much misinformation in this thread!
First of all, cleartype will work better on higher resolution displays - if the display is so low res that the pixels are too visable, then it'll just make things blurry - the finer the pixels, the better it works.
DIV / not-DVI - makes no difference apart from the usual 'DVI gives a sharper picture', which might mean in extreme cases that a particularly bad VGA connection was already so blurry you didn't need cleartype to get the same effect.
As mentioned above, if you're running your LCD an non-native resolution, then fonts are going to look crap no matter what you do, cleartype or not. Best thing to do about this is change back to native resolution, and if the fonts are too small for you, change them in the windows properties (you can get very good control over them if you go into the advanced section from the Apperance tab). After doing that, then try cleartype.
Not everyone will like the effect. Took me a while to decide I liked it. Again, your preference will probably change depending on the display resoluiton/size.
Also, may need to tweak what it does depending on the display pixel arangment (i.e. how the red/green/blue cells are laid out). The best method of doing this, and of changing the effective contrast of cleartype, is a nifty (and free!) program called cleartweak. It is also very useful for quickly turning cleartype on and off - handy for a laptop that you also use connected to a CRT :
http://www.ioisland.com/cleartweak/