I have been using Zoho CRM on and off for several years. I have used it both as a free and paid service (my needs have changed during that time and Zoho lets you up and downgrade as you need).
In my opinion, Zoho CRM gives a lot of bang for the buck and I wholeheartedly recommend it to anyone who needs to follow up with customers on a regular basis.
Zoho CRM lets you document all relevant information about customers and potential customers, helps you to keep leads in the forefront of your activity, gives plenty of reporting options and additionally has a ton of flexible setup options like adapting the screens to show only the fields you need, changing field names and exporting data. I have used the export option extensively to get the required mailing info for an external emailer application and it has worked very well.
Deserves 5 stars.