ksetispy has a built in cache system. Yes it is for KDE, but will run under GNOME if you have the proper libraries installed. It looks exactly like SetiSpy for windows, but has more features.
For my system, I just use the command line client connected to my internal setiqueue server and I like it better than running a seperate cache on each of my machines.
Also, GNOME has a Seti Applet that works pretty well when combined with setiqueue. It displays a ton of information on a panel and has several nice configuration choices built in.
There are a ton of others you can use. I personally have used the Gnome Seti Applet when I used to use GNOME, and KSetiSpy when I switched to KDE. My times in GNOME were 4:20 and my times in KDE are about 3:50. GNOME is more of a resource hog that KDE. I now just use the command line client and leave it minimized while having it connected to my setiqueue server.
When running seti with no desktop manager (command line only), my times are roughly equal to my times in KDE 2.2.2. I would suggest getting KSetiSpy and running it in KDE if you want to have a nice GUI AND cache built in.