I have been using it for a few months now and love its ease of use for both me and my clients. It tracks payment and you can run reports on your client payment history. Like Bridie, I have it linked to my PayPal account so payment by credit card is a snap. I don't use the tracking feature as I do this manually but the timer functionality is pretty good. I also like the presentation of my invoices. I am happy to recommend it based on my experience.
Clockwise Virtual Assistance