Need advice on performance troubleshooting

Hi folks! :-) I am experiencing a gradual performance drop problem --- having a machine running 24/7, after some time (say, two weeks) the system becomes increasingly slow, in terms of desktop response. It takes several seconds (cca 15-20) to open an "open file" dialog in a text editor, or a new terminal window or such. The window takes 2-4 seconds to gain focus after I click on it. If I move the mouse over a typical toolbar, it takes a second or two for the particular button to get highlighted, and the highlighting "rectangle" follows the mouse like 2-3 buttons behind. Clicking on a new message in KMail takes 1-3 seconds to actually display it. Most GUI stuff becomes increasingly (and annoyingly) slow. There is enough processor power, according to top and other diagnostic tools. Besides, compiz happens to remain completely responsive --- cube, this, that, all effects are fast and snappy. Mplayer runs flawlessly. But the rest of the GUI starts to drag. The text selection in an editor follows the mouse with 1-3 seconds delay. And such stuff... On a freshly (re)booted system everything is fast and snappy for a couple of days, and then it gradually starts to get slower and slower. This coincides with increased usage of swap, which tends to rise from 0 to 1.2 GB in two weeks period. I suspect that swapping is partially the culprit for performance degradation, but I am unable to determine what app is using all that swap, and for what. I would appreciate any pointers where to start looking for this swap drainage. Also, if I try to run the system without swap (disabling it manually right after boot), it starts to choke after some time, and I need to reboot it. The hardware has 2GB RAM, 4 GB swap, core 2 duo @ 1.5 GHz. I use the machine for usual desktop activities. Typically I have several apps running non-stop: firefox (3-4 tabs), kmail, ktorrent, kile, couple of konsole instances, two skype instances, cairo-dock, xmms and okular. The desktop is 64bit F12, KDE, running compiz/emerald. I have several usual plasmoids on the desktop, nothing too fancy (clock, graphs for cpu, temperature, battery, network and RAM usage). Occasionally I start other stuff (krusader, quake3, Wolfram's Mathematica, other infrequent things like photo editing stuff etc.) but I shut them down after usage. I notice the slowdown even if I don't use any of that. The symptoms appear like something is leaking memory --- slowly (noticable only after two weeks of continuous running), but cumulatively. This triggers gradual swap usage, which then gradually decreases performance and responsiveness of the whole desktop. I tried shutting down all desktop apps, and this releases some swap (but not all?!), but the system remains in a bad shape, which is visible if I (re)start any app again. Things like mplayer run flawlessly, but it takes cca 15-20 seconds to start the Konsole from which I can invoke mplayer. Once I left the system running unattended for a month (I wasn't at home), and I accessed it only via ssh a couple of times (without problems). When I got back, the desktop was so slow and unresponsive that I couldn't even wait for it to do a regular shutdown/restart, and instead I pulled the plug and rebooted it fresh. When I try to shut down a multi-tab app (firefox, kile, konsole), it takes so much time to close itself that I get a dialog saying that the app is not responding (and offering to terminate it). If I just wait, eventually both the dialog and the app close themselves. It can take them from 5 seconds to half a minute do close, depending on the shape of the rest of the desktop. I'm at a loss where and how to look for memory and performance drain. My current uptime is $ uptime 02:04:55 up 14 days, 4:54, 6 users, load average: 0.62, 0.55, 0.39 and I can feel the slowdown quite easily. I'd be happy to hear any advice on how to troubleshoot this, before I get pissed off and reboot the system again. I'll also gladly provide any additional info. Thanks, :-) Marko