This shouldn't be too surprising, given that RIM forked over more than half a billion dollars to NTP. Anyone with even a small chance of succeeding in suit against RIM is likely to follow suit if the potential gains are that large. To be fair to Visto though, unlike NTP, Visto is a functioning, consumer-oriented company that is providing a service to the market, and they claim that their goal is an injunction against RIM to take BlackBerries off the market and thus protect their good.
It'll be interesting to see where this goes. According to the NY Times article, RIM is again stating that they (a) don't feel that they are infringing, (b) feels the patents are invalid, and (c) have a workaround ready anyway. But I'm sure we're looking forward to another protracted legal battle here.
The market, though, doesn't seem to have an initial strong opinion of the impact of this lawsuit. RIM stock started the week at 76.80 and closed yesterday at 73.03 for a drop of only 0.5%. (As of 11:30am on Tuesday, it had dropped another .4 points.)