I started using BaseCamp and I'm liking it alot. There seems to be alot of flexibility with the product that I like and the permissions are extremely easy and simple to set up. If you operate a multi-va business, there is a time tracking feature built in (it's available with the Plus version). They do offer a free 30 day test drive, so it may be worth checking out.

Prior to that I used MS Sharepoint for about a year. Sharepoint was easy to navigate, probably because it's familiar Microsoft, but it was taking forever to customize the way I wanted it. Plus I'm kind of anti-MS so I wanted out.

I like using project management software because it gives me a true handle of where I am on projects and where my subcontractors are on projects. It took a little while for the clients to get used to my system...well the ones who have been with me for years, but now it's second nature. They are extremely impressed that they can see what's going on at a click of a button.

-B