I would ABSOLUTELY say it's worth it. In my experience with the standard battery, if I didn't charge the phone at all during the day, I would make it home at 5 PM with under 25% battery remaining. This was with 4G turned off. I would classify myself as a moderate user. Also at this point, the "new phone" factor has worn off, so I'm not constantly touching it. I don't have the phone to my ear all day, and I'm not constantly on facebook on it, but I do listen to XM radio from ~9 - 11, then again from 3 - 5. In between I typically have dog catcher playing podcasts, so while the phone isn't on, it's not sitting idle either. I have disabled facebook notifications, but I do have gmail and corp mail pushing to my phone (corp mail is through Touchdown).
After the extended battery, I leave 4G turned on all the time, as well as bluetooth and WiFi, and under the same scenario, I get home with well over 50% left. I have actually let the phone sit mostly unused on a weekend day while camping (decent 3G signal area) with everything turned on, WiFi on but no hotspot in range. I did grab it a few times, made a few phone calls and sent a few texts. Battery was at 35%, but I had 22 hours since it was last plugged in. For my money, that's AMAZING battery, far better than anything I had on my DroidX, or the iPhone 3G (when I had that).
If you can get the battery for $25, get it. I'd even say that at full price, for the improvement I've seen, it would be worth it.