My tablet beta site has some older Cisco 1242 and 1240 independent AP's.  Most of these legacy Cisco AP's do not have the 802.11d country code enabled by default, and many sites with this generation AP don't change that setting.  I was able to have Dave L from the Tablet Engineering team travel to my site.  He was able to show me that the tablet is engineered to operate best with 802.11d enabled.  When it is disabled, the tablet radio has to scale back on power for probes so it does not violate any regulatory issue.  The net affect of using the ET1 at a site with 802.11d disabled is that it will have a much smaller, if not blank, AP candidate list.  We could see the tablet roam triggers happening, but there were not candidates to move to.
 
Short term fix is to make sure your sites have 802.11d enabled.  With that setting, the tablet should roam very well.