I am working with Ubuntu 7.04 and have not had any performance issues. Does everyhing work more slowly for you, or only specific things (like opening a model, zooming in / out, starting the application, opening the application in the browser etc).
What hardware are you using? Can you tell weather it's a CPU or disk issue? (Do you see high CPU usage or high disk usage while you're waiting for something to happen?)
For best results, use the Firefox browser..