How do I find out if there will be a fsck during the next boot?

It depends on your filesystem, in addition to /forcefsck .

With ext2, ext3 and ext4 you can use

dumpe2fs -h /dev/diskname 

Where diskname is for example sda1. You can determine name of your disk partition by running command

mount

Example output (only partly):

/dev/xvda1 on / type ext3 (rw,noatime,usrquota,errors=remount-ro)

Where xvda1 is name of root disk partition.

For dumpe2fs three interesting items are

Mount count:              9
Maximum mount count:      36
Next check after:         Mon Feb 14 09:31:33 2011

Ubuntu will run fsck if mount count is equal or greater than maximum mount count, or if "next check after" is passed.

Starting in Ubuntu 11.04, this information will be shown in your /etc/motd file, using the tool /usr/lib/update-notifier/update-motd-fsck-at-reboot, which checks ext2/3/4 partitions for both date-based and count-based auto-fsck events. You can run it manually like this:

sudo /usr/lib/update-notifier/update-motd-fsck-at-reboot --force

and it will report any partitions that will be checked on the next reboot.

There's a utility called showfsck that will tell you how many mounts are left until the next scheduled fsck.