server OD account issue

we use Apple Lion 10.7.4 server, and setup OD, we have 50 end users and we setup 1200MB Quote for each OD user.

end user use iMac, and join this OD. we setup security policy for each iMac. such as passwork policy, screen shoot

we have issue:

since this OD account user work several days, the client iMac system will be very slow, and opened wensite will be close auto. some application will be closed by system always.

also we found user's home folder used space is increasing, even we didn't do any action in iMac.

so how can we fix this? can we save file in local disk? not in server. I think save in server is big problem in bandwidth and system preformance if end user's quantity is big.

Any people can support me?