Gmail allows you to access your email from desktop based applications like Outlook and Thunderbird using IMAP and POP3 access, you can also use the Gmail system as a backup system by adding it as a drive in Windows. Managing contacts is a different thing, to manage your contacts you will have to physically login to your Gmail or Google Apps account.
iContact is a free software tool for Windows that allows you to access your Gmail address book from your desktop. You can find your contacts very quickly without the need to login to your GMail/Google Apps account everytime.
Your contacts, wherever you want them
iContact allows you to manage your contacts from wherever you want, it acts as a central repository for all your contacts.
Manage Contacts from Multiple PCs
If you have more than one PC, iContact will allow you too see your contacts on all computers without the need to synchronize them.
Integration with Emails Clients, Messenger, Google Maps and more
iContact is connected to different tools on your desktop: You can start your email program by clicking on their email address, call them with Skype or find their address on Google Maps and send it to your Garmin or TomTom navigator.
Available as a Portable Edition
iContact is also available as a portable edition, so you can easily manage your contacts from a pen/flash drive with ease.
Overall iContacts looks like a good tool and fills in the void of managing your Google contacts from anywhere.