Hi Rob,
I haven't encountered problems related to compression yet.
My view is that there are three considerations before using compression on the 
client:
1) If the client has enough processing power you can use compression. wouldn't 
recommend it for 286, 386 or 486 clients if it's not absolutely necessary.
2) If your network speed is high enough I shouldn't use compression. It can 
slow down your backups. You should test this in your environment. Just take a 
large file and backup it twice, once with compression=yes and once with 
compression=no and measure the elapse time. My experience is that one should 
use compression over a 4 Mb. Token-Ring network an one should turn of 
compression when using 16 Mb. Token-Ring, 100 Mb. Fast Ethernet or equivalent 
networks.
Because decompressing files is less CPU consuming restoring compressed files 
over a slow network will probably be faster than restoring uncompressed files 
over a faster network. Again, you should test this.
3) If your do not compress files you server's primary storage pool will much 
sooner be filled. You will also probably use more tapes, unless you have a tape 
unit which uses hardware compression (like 3490, 3495, Magstar or Magstar MP 
units).
Kindest regards,
Eric van Loon