The way to tell what a directory entry actually is would be to examine the long listing from the 'ls' command:
From my ubuntu system, I did an 'ls' of a few files just to give you a bit of an explanation.
$ ls -ld /dev/{xconsole,hda,null,cdrom} /dev /etc/passwd /var/run/mysqld/mysqld.sock
drwxr-xr-x 12 root root 14480 2005-12-31 07:35 /dev
brw-rw---- 1 root cdrom 3, 0 2005-10-30 21:09 /dev/hda
crw-rw-rw- 1 root root 1, 3 2005-10-30 21:09 /dev/null
lrwxrwxrwx 1 root root 3 2005-10-30 21:09 /dev/cdrom -> hda
prw-r----- 1 root adm 0 2005-12-31 14:30 /dev/xconsole
-rw-r--r-- 1 root root 1438 2005-09-18 17:39 /etc/passwd
srwxrwxrwx 1 mysql mysql 0 2005-10-30 21:09 /var/run/mysqld/mysqld.sock
When you do an 'ls' with the '-l' command you get the permissions and other attributes of the files listed. With regular files like /etc/passwd you only see file permissions,
-rw-r--r-- which translates to User has read/write permissions, Group has read permission, and Others have read permission. But if you look closely and if you remember from seeing other listings of files, there is one extra space beyond the 9 required to show Read, Write, eXecute permissions for User, Group, and Others. That first space is an indicator of what kind of file it is.
Regular files won't have anything but a dash usually.
Directories will start with a leading 'd' as /dev has above.
Block device files start with a leading 'b' as /dev/hda has above.
Character device files start with a leading 'c' as /dev/null has above.
Symbolic Links start with a leading 'l' (that's ELL) as /dev/cdrom has above.
Pipes (FIFO's) start with a leading 'p' as /dev/xconsole has above.
Sockets start with a leading 's' as /var/run/mysqld/mysqld.sock has above.
Generally I've not had much sucess with finding usable data in the lost+found directory. Sometimes you might get a snippet of something though and when you do, you're really glad that it was there. If anything it can help you decide what needs to be updated on your system (if you're using rpm and such) because you can sometimes determine if certain packages were corrupted and then have rpm re-install them.
Hope that helps.