http://www.softpedia.com/reviews/windows/Portable-avast-Review-54885.shtml
Nice review! 
Yes a nice review, shame about this comment though.
The "small" version of avast! is just as powerful as its desktop correspondent. There is no adware or spyware scan engine available as the product is limited to catching viruses running loose on your portable drive and disturbing your activity.
The adware and spyware signatures continue to grow at a pace, so should afford limited anti-adware/spyware protection but not as a dedicated anti-adware/spyware application would.
The "small" version of avast! is just as powerful as its desktop correspondent. There is no adware or spyware scan engine available as the product is limited to catching viruses running loose on your portable drive and disturbing your activity.Another reason to add an antispyware/antiadware module into avast and not only signatures. Besides, this module could monitor the Windows Registry... Hope they add this in avast 5 version.