If I try to use vi in one of my VEs, I get an odd error, but the 
/proc/user_beancounters don't show any errors, so I'm not sure what I'm 
exceeding.

Here is the error vi spits out:

E297: Write error in swap file
E303: Unable to open swap file for "rc.local", recovery impossible
"rc.local" 17 lines, 387 characters
Press ENTER or type command to continue

and here is my user_beanconters immediately after I quit out of vi:

root@ftp:/var/run# cat /proc/user_beancounters
Version: 2.5
       uid  resource           held    maxheld    barrier      limit    
failcnt
      106:  kmemsize        1167508    1524641    2752512    
2936012          0
            lockedpages           0          0         32         
32          0
            privvmpages       14146      21232      40960      
81960          0
            shmpages             57         57       8192       
8192          0
            dummy                 0          0          0          
0          0
            numproc              30         39         96         
96          0
            physpages          2798       3561          0 
2147483647          0
            vmguarpages           0          0       6144 
2147483647          0
            oomguarpages       2798       3561       6144 
2147483647          0
            numtcpsock            6          8         80         
80          0
            numflock              1          4        100        
110          0
            numpty                1          1         16         
16          0
            numsiginfo            0          2        256        
256          0
            tcpsndbuf             0      51060     319488     
524288          0
            tcprcvbuf             0       2220     319488     
524288          0
            othersockbuf       4440      10000     132096     
336896          0
            dgramrcvbuf           0        684     132096     
132096          0
            numothersock          4         12        120        
120          0
            dcachesize            0          0    1048576    
1097728          0
            numfile             582        731       2048       
2048          0
            dummy                 0          0          0          
0          0
            dummy                 0          0          0          
0          0
            dummy                 0          0          0          
0          0
            numiptent            14         14        128        
128          0

It might be something really obvious, but I'm not seeing it :-(

This doesn't happen in all of my VE's so I guess it must be something to 
do with the amount of memory I have allocated to this one (or 
something), but nothing seems to be getting too close to the limit.

Steve