I found this info just now.
ACiD sync can sync you're data from and to memory cards, something which isn't possible with ActiveSync, yet.
"ACiD Sync is a file synchronization utility designed to work with devices dubbed by Microsoft® as Smart Devices. These devices include Pocket PC's, Smartphones, some Treo mobile phones and the new Motorola Q series. ACiD Sync enables the ability to synchronize files stored in a "My ACiD Sync" folder on the Desktop PC with a corresponding "My ACiD Sync" folder on an external memory card of a Smart Device─a capability sorely lacking with Microsoft's® own ActiveSync® desktop synchronization utility. These files can be of any type and any size ─ ACiD Sync can do 'em all."
The idea comes from Ed Hardy from the Brighthand website.
Get it
here