I've been developing web and win apps for the retail and financial market for many years and I've found SQL to be very valuable and T-SQL an easy language to work with.

I've put a great deal of time learning as much about SQL as possible (to the point where I've often been asked for advice from DBAs in companies I've worked for!). This has resulted in me being able to write some great applications. In retrospect, if I didn't have the SQL knowledge I currently possess would those apps have been as good? Simple answer - No.

I feel SQL can sometimes be given a low priority in the personal learning curve of developers. A message to those that do give it a low priority - give it a lot of focus and learn as much as possible and you'll come to find it time very well spent. You might not agree with that now.. but you will do!