[xubuntu-users] Karmic Speed Decreases with Uptime

[Robin]

Output of "top:"

top - 10:20:11 up  4:54,  2 users,  load average: 0.01, 0.08, 0.07
Tasks: 118 total,   1 running, 117 sleeping,   0 stopped,   0 zombie
Cpu(s):  4.0%us,  2.0%sy,  0.0%ni, 91.1%id,  2.6%wa,  0.3%hi,  0.0%si,  
0.0%st
Mem:    507648k total,   254120k used,   253528k free,     8396k buffers
Swap:   995988k total,    11216k used,   984772k free,   107324k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  
COMMAND           
 1280 root      20   0 49440  18m 8196 S  2.7  3.7  11:47.45 
Xorg              
 1418 robin     20   0 17952 7288 5840 S  2.0  1.4   6:48.75 
xfce4-systemloa   
 2537 robin     20   0 31416  12m 9192 S  0.3  2.6   0:00.40 
xfce4-terminal    
 2557 robin     20   0  2464 1156  884 R  0.3  0.2   0:00.01 
top               
    1 root      20   0  2528 1260  988 S  0.0  0.2   0:01.25 
init              
    2 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
kthreadd          
    3 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 
migration/0       
    4 root      15  -5     0    0    0 S  0.0  0.0   0:00.01 
ksoftirqd/0       
    5 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 
watchdog/0        
    6 root      15  -5     0    0    0 S  0.0  0.0   0:00.14 
events/0          
    7 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
cpuset            
    8 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
khelper           
    9 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
netns             
   10 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
async/mgr         
   11 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
kintegrityd/0     
   12 root      15  -5     0    0    0 S  0.0  0.0   0:00.05 
kblockd/0         
   13 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 
kacpid            

It's a Dell Dimension, Celeron D, 512 of RAM. I have Xubuntu 9.10 (ext4) 
set up in 10 Gigs as "/" 1 gig of swap and the rest (69 gigs) as "/home."

If I stay busy on the 'puter, it runs fine. If I step away for an hour 
or more, it slowwwwws dowwwwwnnnn, lol. Not badly, really, but 
noticeable.  When Firefox takes 20 seconds or more to load, though, I 
shut down and walk away for awhile. On startup it goes well again.

Maybe it's just heat?

Sorry, n00bish question probably.

-Robin