I have used SalesForce (SF) for tracking leads. Hundreds of professionals use it for tracking leads. Some of the features:
1. Allows you to sort on any column (date, sales price, address, zip)
2. Since Excel is not for everyone, it's more user friendly, since you are not crunching numbers and thinking of cute formulas, just sorting after you enter the info,
3. Allows you to put leads in stages, such as 25%, 50%, etc. As you do that, it calculates your sales volume in total dollars.
4. Allows you to sort leads by priority or stage. For example, a lead may be a 1 when you first talk to them and move to 10 when you actually get the property listed.
5. Everything can be exported to Excel.
6. My favorite item was sorting by zip code. I could manage my contacts by address, calling on several in one day, or contacting several in one day in close proximity. I used a Fujitsu Tablet and it worked great with this part of it.
I was doing business prospecting (selling software) and it worked well. I used it 3 or 4 years ago, so I'm sure it has improved. Another advantage is it is an ASP (Application Service Provider) based service, so you can access it from any computer. It is also a huge company, it just acquired Jigsaw. Other companies are building apps for SF including http://www.activalive.com/salesforce and Docusign. The problem with CRM as Spring mentioned is that it is not always simple. Once you learn it, it can be powerful though. I guess it depends on how many contacts you are trying to manage. I have over 1000 and do mail out campaigns every month or two, for 500-1000 addressees, so SF may be best.
Lastly, you can assign permissions based on role. The owner of a company could have the top level, then see the leads for individual agents. The agents wouldn't be able to see each others leads, and so on.
I may try TimetoNote as mentioned above. One entry point is ideal, and I use Google for other apps. I have used BaseCamp for tracking projects, it works very well for assigning tasks and managing time lines. Another one to look at would be Gist. It pulls the contacts out of your email for you. It works with GMail and Outlook.