My view on the slow restore problem is that it is down to the tape
technology. I've done quite a bit of testing with restores on AIX, NetWare
and NT and can say the following:

1. I can rule out the network and server performance as the bottle neck.
Doing a full backup and restore will give comparable performance and ADSM
will run as fast as the network will allow. Also as fast as any other
product (Arcserve, BackupExec).
2. Large filesystems containing large files will give a reasonable restore
performance. Large filesystems with lots of small files give a terrible
restore performance.

What I think is happening is this:
Due to the incremental forever backup method the files are becoming
fragmented on the tapes. A file changes so a new version is written to the
tape. The oldest version is then deleted  leaving a gap on the tape. The
problem with fragmented tapes is that the seek speed of the tape drives is
very slow. Some are better than others, I've found Magstar  3570's are
quite a bit faster than DLT's. So when we come to do a full restore the
tape drives are spending most of the time searching rather than
transferring data.
Arcserve and the like do not have this problem as they are generally setup
for a weekly full, daily differential so are able to stream data off the
tapes in one big block and are only really limited by the transfer rate of
the tape drive.
The probem with ADSM has really got worse over the last few years due to
the amazing growth in disk capacity/price. It is now becoming a real
problem when we have these big fileservers going in.
I'm not sure what the answer is. Some things that can help are to make sure
you are collocation on your tape pools and run regular reclamation to
reduce the fragmentation.