In addition to the privacy concerns stated above, I'd just like to add that this causes a *huge* hit to usability. There is already a lot of information presented in the dash home, and adding a stream of information that is probably totally irrelevant to a given search goes against the whole point of having the dash - namely to find stuff more easily.
Example: I keep a journal on my computer. It is a file named journal.odt. If I type in journal, I just want to see that journal (and maybe some relevant programs, like Gnome Activity Journal). I don't want to see icons for: "Hand - Deadroom Journal  $7.77"; "Taylor Dupree - Journal  $2.79"; "Bridge 61 - Journal  $8.99"; "Jully - Journal Intime  $9.99"; "Arabica - Journal  $9.99"; "Dday One - Journal  $2.79... and that's just one line.
That this turns every desktop search in to an advertisement threatens to make Ubuntu seem like adware itself, as vexorian mentions above, but even if one finds these options useful, the amount of clutter added to the dash home is a problem.
Making this a separate lens would solve both these issues to an extent, since if the user went specifically to the shopping lens there would at least be the assumption that the user wants to actually buy something. Integrating it with the home lens makes no sense since the vast, vast majority of times a user types something into the dash they don't want to buy something new, but rather want find something that is already on their computer.
This, coupled with the privacy concerns mentioned above (which are really, really serious), ultimately means that even a separate lens should be an *opt-in* feature - especially considering the vast majority of users will have no clue how to disable it.