I'm sorry, I didn't know that /opt was already mounted on /home/users.

Yes...right for some applications. It was just a workarround, not the perfect solution.

But :

If /home/users is on the same card of /home/users/MyDocs, what about shrink /home/users/MyDocs and expand /home/users ?

If /home/users is on a separate card of /home/users/MyDocs, what about shrink /home/users/MyDocs and create a second partition (ext3) in it at /home/users/soft and move /opt link to this new point ?

Finally, there's a lot of possibility for advanced users...but when the N900 will be released is there a hope that all this mess could be different ? If not, I think that a configuration widget for end users could be necessary [and | or] a modification of installation process of extra packages could be refused if they are not "optified" [and | or] something else...let's start brainstorming