There was a great post today on Lifehacker about using Gmail as a hub for all your communications. Its something I'll be looking into over the weekend, although its a little overkill for my needs. For anyone using an Android phone Gmail, Google Voice and Gmail's contacts list are well worth tweaking out.
In particular, it isn't too hard to consolidate all of your contacts into Google Contacts. There are a number of sites that help in this respect and one that I've used and found satisfactory is Gist.com. Gist will take all of the contact info from any accounts you let it access, including actual emails and consolidate that information into a database. Gist will also take email addresses from your contacts and look for other accounts on various sites under that identity, i.e. Flickr, Myspace, etc... From there you can export your contacts database back into Gmail and all of your contacts will be in one spot. A nice feature is that the various contacts can be tagged depending on their source. Once your Google Contacts are updated you can then import that database into your other accounts such as Facebook and Linked In. The whole processs isn't seamless, you get some duplicates and not all of the info gets transferred but overall its a useful tool.