While I agree with the thinking here, simply learning Photoshop and CSS doesn't make you a designer and learning programming doesn't make you a programmer. I'm a front-end dev who's more than competent in Photoshop and can write really modular, daresay good CSS but if I had to decide between using a designer or making my own design, nine times out of ten, I'm going to use someone who is, by trade, a designer and has an eye for crafting a beautiful UI, choosing colors, and for laying out type.

I'm slowly but surely getting better at design things but I choose to focus my energy on development rather than prettifying pixels (I say that with absolutely no intent of malice).

I agree that broadening my skills to include design would be helpful. I'd also be really great off if I learned how to treat my own ailments and fix my own car. I can't do it all though, so when I have the need, I partner with designers. I look through portfolios, gauge talent and ability, and hope for the best.