You never know where a  'hobby'  will lead.  If you get hooked on digital imaging like I did, you will be glad you spent your time learning the application most pros use - Photoshop.    In addition, you're plugging into Adobe, which means easier crossover with applications like 
In-Design, ImageReady and now Dreamweaver.  

My interest in digital imaging started as a hobby 4 years ago, and now I'm looking to do it as a living.   I've never regretted learning Photoshop, and at times, give a sigh of relief I chose it.   There is so much professional community support on the web, in books, in 3rd party products, in Adobe support.  

It seems to me investing your time learning Photoshop gives you far more options should your 'hobby' turn into a passion.