We could. It has been mentioned before. I don't think it is necessary (although it couldn't hurt) because litigious or not, I don't see how a case could be made that "the Internet cost me my job and got me in trouble with the IRS". I am not a lawyer however.
Moreover, I wouldn't want to actually write the words of a disclaimer, and unless StackExchange Inc has some boilerplate, it might be more harm than good (again, I am not a lawyer and it isn't my money). Perhaps an actual SE employee should give us the corporate stance.
Littleadv is a very thorough and accurate poster. I think the same sort of mindset that drives him to write a disclaimer every time is exactly the mindset that gives him the ability to reference specific US Tax documents in his post. Some people are just very complete thinkers. No big deal to read his disclaimers; plus he is technically correct. This is an advice site, but we get what we pay for.
Finally, I think that Littleadv is smart in that people are likely to only read the post if the come from The Googles or The Bings. Members of the site will read the FAQ, but a generic user won't, so the disclaimer needs to be in each answer for a drive by visitor to see it.
From the legal page:
5. Warranty disclaimer
Stack Exchange has no special relationship with or fiduciary duty to
Subscriber. Subscriber acknowledges that Stack Exchange has no control
over, and no duty to take any action regarding: which users gains
access to the Network; which Content Subscriber accesses via the
Network; what effects the Content may have on Subscriber; how
Subscriber may interpret or use the Content; or what actions
Subscriber may take as a result of having been exposed to the Content.
Not being a lawyer, I don't think SE is getting sued. Are we worried about being sued individually?