As far as I know there is no State Bar requirement or ethics opinion that says specifically that not using Westlaw or LexisNexis constitutes a violation of professional responsibility. One can still Shepardize cases the old fashion way (hopefully your county law library still subscribes to the print version.) And, although the theory behind having Westlaw or LexisNexis is that it makes your legal research easier, there is also the perception that not having such a tool exposes you to malpractice issues. But does that perception match up with reality?
Let's say that instead of spending thousands of dollars for Westlaw or LexisNexis (or Bloomberg), how about if I rely solely on one of the more basic research tools? In Texas, one of the benefits of being a member of the bar is having access to "Free Legal Research". Any problems with an attorney relying upon this service as his or her sole source of online legal research? Are you already doing this??