Hi,
I would have to agree with Tess. I just celebrated my one year in business and didn't increase my rates for existing clients but have increased my rates for any new clients.
I haven't had someone leave for a rate increase...but that would be because I haven't increased my rates!
I have worked weekends on occasion and I would charge more. I have noticed from viewing others websites that they do charge more for weekends and or rush orders.
I hope this helps!