I followed my own advice yesterday and upgraded to a 22 inch screen from my 19 inch. My reasons were specifically to do with bad software that requires at least 1024 pixels in the vertical, but the extra screen real estate of 3 inches, 150 pixels vertically, and 210 pixels horizontally does come in handy.
If you needed any other reason to do this, you should just look at the prices. Now I do not promise that these screens are the highest speed and quality in the world, but you can now acquire a 22 inch screen for £130 inc VAT in the UK – which compares very favourably to my first 15 inch LCD at £349 inc VAT back in 1999.
You know you need it, and hey I am looking now at USB-Display Link adapters to see if I could drive a 3rd screen of this resolution.