I have been making large multi-panel photo mosaics of the bird of South Gippsland, using South Gippsland scenes as the tiles for a while now. Whilst Mosaic Creator seems to do a reasonable job whatever you throw at it, I have the overwhelming view that Andrea Mosaic gives me more creative control (but alas with that comes the ability to really ruin images as well) and I got top thinking I should treated making mosaics more like painting an image. Then the penny dropped I needed to get a better palette of colours, from which to mix my new Mosaic, just like an artist selects his tubes of paint and makes up his colour scheme. fd's Flickr Toys has a neat palette generator, I think it is really meant for web designers or home decoration projects. It is so easy to use I don't need to explain that here. All you need to do is upload a photo and a palette of colours based on the colours in the photo will be generated automatically.
So next I looked through my picasa library of photos (many 1000s) using the tools/experimental/search for.../blue, etc which shortened the search tyime considerably and exported those images I thought best matched the palette. In this export I also reduced the size to 800 by 600. Then I fired up andrea mosaic created a new library of tiles with the photos I had selected, which reduced the tile size further. Now I used picasa again, to make a 200% poster, which blew up the image and made it into four parts. Finally I created mosaics out of the four image pieces using andrea mosaic. I am very pleased with the outcome.