When I looked for something to sync a PocketPC to my Mac a few years ago the two main products I could find were PocketMac and Missing Sync.
I bought PocketMac - it sorta worked, with alot of futzing around it synchronized once or twice (saved my addressbook) but it was never consistent.
This was with an older Toshiba e755 PocketPC and a G3 and later a G4 iBook (both of which will soon be for sale)
I got sick of the futzing (and a long period of not synching) and I tried the Missing Sync with my MacBook and the same old Pocket PC... no problems at all.
I can't say that the PocketMac software would not have been fine with my newer laptop - but I know from reading the support forums that removing PocketPC can be a task, and one that has to be done before installing Missing Sync - so I tried out the Mark/Space software and it has been great so far.
Your mileage may vary - I've read postings from users who have had no issues with PocketMac, some people are quite happy with the software, but I wasn't one of them.
Yeah Markspace has been quite good for me so far, and I'm pretty sure I'm going to stick with it after hearing about PocketMac... Its unfortunate that the isync doesn't seem to work with the wm5 devices.
I'm also thinking that $40 is $40 that I could spend on an iphone accessory once I head down to the states in October... decisions decisions...