The product is good, with very good ease-of-use and interface. Secure screen sharing and data transfer via SSH works well.
One thing is missing for a true remote control: if the remote computer shuts down and restarts, there is no way to log in since ShareTool only starts working once login is done. So login must be done with a competing product, e.g. Timbuktu, which fills this gap. This feature seems indispensable to me - if I want to control a computer remotely, I want to stay in control!
Minor bugs which have cropped up from time to time have been fixed. Right now there is a problem with interaction with the KeyChain in Snow Leopard which will no doubt be fixed soon.
The product advertises on-the-fly compression for data transfer, but is nevertheless no faster than a competing product (iGet) which doesn't do this.
Upon sharing, ShareTool can alert the start of sharing via e-mail. However, the e-mail gives only the local IP number, which is useless for connecting via port forwarding if the remote computer is behind a router with dynamic IP address. It should also give the external IP (like GetMyIP or DynDNS) and include it in the e-mail.