Now a days Digsby Installer is coming with InstallIQ. So you will have to accept the TOS of Digsby and InstallIQ if you want to install the Digsby. If the InstallIQ is installed on your machine, it will write a unique ID to the registry, and that key will be used in other sites to identify you and your activities.
Read some thing below
1. InstallIQ will be installed with Digsby, You will have to Uninstall the InstalIQ if you want to remove the registry key (Uninstalling Digsby may not remove this)
2. Digsby is Free and it means that optional softwares may come with the installation
3. It will try to change your home page, Search engine, install a tool bar too.
InstallIQ Terms and conditions
few lines from that
By accessing the Sites and downloading the Content, you hereby grant us permission to display promotional information, advertisements, and offers for third party products or services (collectively "Advertising"). The Advertising may include, without limitation, content, offers for products or services, data, links, articles, graphic or video messages, text, software, music, sound, graphics or other materials or services.
You must provide valid and accurate information about your identity including a valid email address. You may not use another person's name or information on our Sites. You agree to use the Sites and Content only for lawful purposes.
Pricavy Policy of InstallIQ
We collect information you choose to submit, for example, when you download one of our products, subscribe to our online services, or participate in a survey or contest.
We use the information you submit to provide our services including the presentation of personalized content.
So think of these issues, Read the TOS of both Digsby and InstallIQ well and then proceed.
If you want an installer without InstalIQ it is here (Installing Digsby alone)