unionfs on CURRENT for read only OK?

Hi

The man pages for unionfs basically say to avoid it as it has problems. 
   However, I was wondering about people's experience with it for read 
only mounts.  I would like to do a bunch of read only mounts.  I 
currently use nfs with localhost: but think that performance might be 
better with unionfs.  I kind of get the impression that the unionfs 
problems are with read write and so would like to solicit opinions and 
experience running on FBSD5 (CURRENT going to 5.3-R).

Thanks
Chad