I used to use ImageShack and only turned to Flickr so that I could get used to it for a PDF tutorial I'm working on for Photo of the Day. ImageShack in quick and easy, but doesn't really give you much in the line of photo sharing options. Flickr has a good online photo sharing community and options. IS is easier to use. With the ImageShack Downloader app, all you do is drag the photo to the program window, select some size options and upload. It will return a window with the links you need to post in MR or other sites. Flickr has improved, but it currently has three different methods of posting that I have been able to figure out so far. The image quality in Flickr seems to be a bit better.
Oh, ImageShack is free with no registration. Flickr requires a Yahoo account (Flickr is owned by Yahoo). 200 images are free. If you have more than that on your flickr page, you need the $25/year Pro account.
The link in my sig will show you how to use ImageShack. Please ignore the Flickr tutorial. It is out of date and will be updated soon. This week I hope.
Edit: If you want to see who uses Flickr in Photo of the Day, run your mouse over a photo. If it "gives you the finger", click it. You will jump to a Flickr page (usually). Ignore the ones that read Attached Thumbnails. They are direct uploads to MR.
Dale