Why should we use GIMP when we can get Photoshop? Seriously, Photshop is just more powerful and professional, also easier to use (really), and plus, has an user-friendly interface, not like GIMP.
For me (but we all haven't the same opinions), GIMP is just for people who are against pirated-softwares, the others shouldn't deprive themselves to use Photoshop, but once again, it's just what I think.