Actually you have a problem: if you have home on NFS, then when you're not connected you won't be able to mount /home, and that's not good.
If you need to use the laptop offline AND the desktops without the laptop, you have 2 choices:
1. use a distributed filesystem like coda or afs. Keep in mind this is not so easy to setup for a novice
2. export the desktops' /home, but keep a local copy on the laptop as well. Then when you connect the laptop, mount //desk/home as /mnt/home and have a cron script run:
rsync -ua /home /mnt/home
rsync -ua /mnt/home /home
You may need to install the rsync package, then see rsync manpage.
PS: the (sync) in the /etc/exports means that writing is syncronous, i.e. the server won't return an ok code until it has finished writing to disk. In async mode (most used on slow peripherals like printers) the process returns ok after having stored the data in a buffer, so the client doesn't need to wait.