Any way I slice this question the answer is no, but I get there sort of circuitously.

Not every lawyer should have a blog, because not everyone is predisposed to processing and sharing information in the way blogs facilitate. Lawyers who answer "yes" to more than one of the following questions but don't have a blog should think about starting one:

1. Do you read or otherwise take in many materials related to your practice, above and beyond what strictly speaking you need to get through your daily workload?
2. Does your practice put you in places and situations that don't get much or any news coverage, but you think others might nonetheless find interesting or informative?
3. Do you email colleagues items you think they might want or need?
4. Do you make lists? (Mentally or otherwise.)
5. Do you spend much time using search engines?
6. Do you write about legal issues or developments for print publications or other outlets?
7. Do you hate the idea of keeping extraneous paper around, but like being able to find and refer to things you've read and found significant for one reason or another?
8. Do you like staying well informed about developments that affect your practice and your clients' lives and businesses?
9. Do you have a sense of humor?
10. Are there one or a few substantive areas of the law you know pretty well, or better yet, very well?
11. Are you sufficiently professional and comfortable in your skin that you will link generously to material — including competitors — that's not part of yourlawfirm.com without worrying that you'll never see that reader again?
12. Are you sufficiently professional and comfortable in your skin that you will publicly acknowledge and correct mistakes?
13. Do you think your clients, potential clients, and colleagues probably already get more email and paper mail than they'd like?
14. Are you less than thrilled with your ability to manage your conventional practice-related Web site and keep it up to date? Are you less than thrilled with its ability to get your message out to colleagues, clients, and potential clients?
15. Are you willing to engage in public discourse with people you don't yet know that will raise your profile and sharpen your writing and thinking, but might not translate directly or immediately into paying work?
16. Are you basically a good egg? (Lawyers who think hiding associate contact information is a good idea, for example, might not be the best candidates for blogging. Then again, it could prompt some sort of "born again" epiphany.)

Law firms are a different story. Before a firm decides to publish one or more weblogs, it and its prospective bloggers in residence (and I do hope they are "in residence," rather than commissioned for the purpose of generating weblog posts) had better be able to answer all of these questions affirmatively. Law firms (like all businesses) aren't a who, they're a what, and blogging (when done effectively) is a who-oriented pursuit. All the firms to date I've seen successfully embrace blogging are small or solo shops. I'm not saying a large firm can't do it, I just think there are more hurdles to overcome in that setting. Until weblogs are mainstream enough that thoughts like these are a quaint anachronism and people just know what works well and what doesn't, businesses (including law firms) should think hard about whether they've got what it takes to do a good "official" blog. If not, following in the footsteps of Microsoft, Sun, and Harvard is worth considered thought — i.e., we're not people but we've got people, spectacular ones, here they are. (I'm also assuming this question was aimed at public blogs. I think most law firms would save all kinds of time, money, and lawyer brain cells by replacing their existing intranets with a network of internal, syndicated, well-indexed and searchable blogs.)