Over the years I have accumulated a database of over 3000 contacts.  They have resided in a number of progams and each had it advantages and disadvantages.  

For several years my contacts resided in Sage Act a contact management system which worked well, especially when I needed to synchronize a sub set of my contacts with another organization. Act is great if your focus is following up on sales leads and you want to synchronize your data with others remotely. Act uses Microsoft Outlook to send and recieve e-mail and that worked well. Although it should have worked, synchronizing with my Blackberry presented some challenges.

As my need to synchronize with others disappeared and my version of Act became outdated I switched back to Microsoft Outlook. I wanted to synchronize contacts with Google Gmail to provide an on line backup and also with my Blackberry. I tried some synchronization programs andCompanion Link worked the best but most attempts at two way synchronization resulted in many duplicates. When one has 3000 contacts and gets duplicates you can easily be looking at 6000 - 9000 contacts which presents a challenge. There are programs to remove duplicates that help but it is not a simple task. The safest way I found was to use Outlook as my master contact database and synchronize one way to Google and my Blackberry. 

Hoping technology had improved I tried using Salesforce.com a few months ago as it would provide cloud backup for my contacts and should let me access and edit them in Outlook and on my Blackberry and iPad. Significant effort was put into uploaading my contacts in batches to Salesforce before an attempt to synchronize could be attempted and only then does one find out  that Salesforce.com is not compatible with the current version of Outlook. They suggested I try third party add ons for an additional cosst and provided very detailed instructions for changing the computer registry which might work but I was not willing to take that risk. I scrapped the idea of using Salesforce.com and decided to look for other options. I know salesforce is widely used by large organizations but they have IT departments to tweak the systems so they will work. 

My latest attempt was to try Plaxo a service which provides cloud storage and synchronizes with all the devices I own. There was not need to upload everything like  with Salesforce.com, just set it up and tell it to synchronize. It did create duplicates but a call to their on line help quickly brought my 9000 contacts back to 3000 where they should be. I have been using it for a few weeks and I believe two way synchronization is working effectively between Plaxo's on line database and Outlook 2010, Google contacts and my Mac address book. I have not been able to make the Plaxo Blackberry app work and I am waiting to hear from their technical support, but in the meantime I am using one way Companion Link to keep it up to date. It is not yet a perfect solution, but it is the best I have achieved so far. 

I hope sharing this might help someone else.