in my opinion it's totally depends upon the user/viewer.
i am using 19" wide screen LCD for last 6 months after using square monitors for last 9 years(still using at workplace).
here are some points i would like to say:
1. widescreen provides more screen area than square. so if you need more screen area - go for widescreen.
2. more and more movies are coming out in widescreen format - so u can go for it if you watch lots of movies.
3. widescreens are very convenient especially for spreadsheets where you can display more on the screen horizontally. for word docs, widescreen doesn't help much.
4. on the other hand, webpages are formatted in a portrait mode and at a lower width than most screens anyway, so you'll probably get little benefit with web viewing in widescreen.
5. today's games are widescreen supported ... gaming is awesome in widescreen monitors too!
6. widescreen really helps a lots of apps like, programming editors, graphics design softwares etc.
So make a list of your work area. then point out which one works best in widescreen and which one suited best for square monitor.
now go for most voted way.
I hope some confusion is gone now.
... That is the the reason why conventional screens are costlier than widescreen for same diagonal size.
This is not true. they're same now.
even if widescreen becomes cheaper tomorrow then it'll be because of popularity or manufacturing cost factor. like, DDR1 is costlier than DDR2