After years of waffling I finally took the plunge and subscribed a couple few weeks ago. My impressions: $15 for a 2 year subscription (plus full archive access) really isn't a whole lot of money, but just the same you can get much more material of equal or better quality for free elsewhere.
The editorials are by-and-large just Loren Wiseman reminiscing about the good ol' days at GDW -- usually pretty interesting, but nothing even close to crucial. The feature articles I've read (which is by no means all of them) are typically of average quality, not IMO up to the caliber of the articles in the old print JTAS or Travellers' Digest, and frequently they're at least somewhat GT specific (which severely limits their usefulness to me). The Discussion Boards are put to shame by these boards, which have a MUCH better interface, higher traffic volume, larger group of active participants (90% of ther posts on JTAS seem to come from the same half-dozen or so posters), and (IMO) more generally interesting/useful topics. Plus, these boards are free.
So, if between this site, the TML, and the various other free websites (Freelance Traveller, Traveller Downport, etc, etc) you STILL feel the need for even more online Traveller, go ahead and subscribe, as the fee is really just nominal. But rest assured that if you choose not to subscribe you're really not missing all that much.