I've been using Investor RT on the Mac for 3 years full time to trade. The software is close to perfect. I can't think of many things I've asked for over the years that the Linn Software team have not integrated within a short period. They are dedicated to total support. E-mails are answered within the same day most of the time.
The only weakness I've found is in the various data services for futures contracts. This is not a problem with the software, its simply a fact that there are only 1 or 2 providers of futures data who give you the accuracy you need to do proper analysis. If futuresource data could be used by Investor RT it would be perfect. If you trade stocks and mutual funds, you will have no problems at all with any of the services.