I've been hearing this question a LOT lately.  People that have been using Screebl for months either get an OTA upgrade to Android 1.6+ (which is where the Android battery usage stat screen first started to appear), or they upgrade to a new device and notice that Screebl seems to be the number one "consumer" of power on their phone.

The short answer is that as far as I can tell the battery stats are wrong.  The reality is that as much as I really do want to own one of every cool Android device out there, I just can't.  Consequently I can't test on all of them. That being said, all indications are that the high reported battery usage seems to be the result of a bug on one or more Android-based devices, most notably HTC Sense-based phones.  In fact, a defect has been identified and reported to HTC along these lines (case number 4102).

More generically, based on reports from Screebl users, it appears that different devices report Screebl's battery usage very differently.  It also seems that the battery usage stats are very often wrong.  A few users of the Droid Incredible have actually tested their battery life with and without Screebl and found that the battery lasted roughly the same  (see the forum thread here:  http://bit.ly/98NRrs).

Here's what I know so far:

• Battery usage is an insanely misleading stat.  Many people assume that it means "80% of my battery was consumed by Screebl", and consequently, "if Screebl were not running, my battery would last 80% longer".  This simply isn't true.  It's not even close.  I've tried to get clear answers from Google on what the stat actually means, but haven't gotten more than "the amount of power consumed by an app when it is running". Screebl doesn't run much.
• Some phones appear to get confused and attribute nearly all system battery usage to Screebl.  This problem is not unique Screebl, and in fact applications such as Locale have started providing disclaimers for certain devices to warn users of the issues.
• Screebl still suspends itself whenever the screen is turned off.  The Screebl service puts all threads into a sleep state using Thread.sleep(99999999999).  It's possible that the Service is still being attributed some kind of resource usage since it hasn't been terminated (even though the threads have been suspended).  I'm looking into this.  At this point from what I can tell, there are no running threads once the screen is turned off...

I'm continuing to look into this, as I'm getting absolutely hammered at this point from a ratings (and consequently sales perspective), but I'm not sure that there is much I'm going to be able to do about improving the battery usage stats on specific devices. 

The bottom line is this:  Screebl either improves your phone's battery life or it doesn't, regardless of what the battery stats say.  On my Nexus One, Screebl averages around 2-3% on the stats list.  Sometimes it goes higher, but will generally drift back down to around that level.