You can rent individual applications from Adobe's Creative Suite directly:

http://www.adobe.com/products/creativesuite/cssubscription.h...

I don't think you'll find any hourly-based software usage although that would be really interesting to see ... something like EC2-running-x-application boxes.

>remote to a server (either Mac or Windows) with Photoshop installed where I could use it for an hour or two for several dollars or euros per hour?

Nope, against the EULA too. http://www.adobe.com/products/eulas/pdfs/Photoshop_On_a_Serv...

Have you tried pixlr (http://pixlr.com/editor/)? It is a very scaled down version of Photoshop, but if your needs are basic it can fill your need and is free. It even has support for .psd files and can preserve layers.

If you only need some hours, why you don't use 1 month trial version? http://www.adobe.com/cfusion/tdrc/index.cfm?product=photosho...

Not a service, but you can go to Kinko's which has retail locations everywhere. And they have high-end printers next to the computers.

Hmm, the question makes me think that rather that wanting to use such a service, the asker wants to build one, and tries to see if there are any competitors.

Pirate it, bitch.