Created attachment 51965 [details]
screenshot of desktop

Version:           unspecified (using KDE 4.5.1) 
OS:                Linux

I can reproduce plasma hanging for a while. 

Just shutdown router or change default gateway to a host in your ip network which does not exist so ip packets get a time out.
Then plasma does not respond. No Kickoff, no program start no mouse reaction to any control bar...

I think the problem could be connected to kopete or skype (I use the skype wrapper in kopete) BUT plasma should never hang even if some application is doing wrong!

The only plasma applets with internet connection is pyweather.

Reproducible: Always

Steps to Reproduce:
1) have a working internet connection (you should have ;))
2) shutdown your router or change the default route to an ip which does not exist, i.e. in linux with iproute2 type as root: 
> ip ro
this should give something like 'default via 192.168.178.1 dev eth0'
then remember the adress and type
> ip ro change default via 192.168.178.123
be sure 192.168.178.123 does not exist in your network so you get time outs
3) wait plasma to hang for minutes with a little wake-up then hang again, and so on until the network connection is available again

maybe you have to open the programs i have (i think it could be skype or kopete (i use the skype wrapper in kopete))

Actual Results:  
plasma hangs for minutes, wakes up for seconds, hangs for minutes,wakes up for seconds,...

Expected Results:  
plasma should never hang

have installed kopete, skype and use the skype through kopete wrapper
gui plasma configuration see screenshot