[woobar]

Not when they are clicking on a link in email or other page.

EDIT: misread your comment. Thought you were talking about mobile apps.

Also, I would not call their mobile site 'very lean'. Just got a single twit page on iPhone: 817Kb.

[untog]

Really? Because when I go to a Twitter link on my phone it redirects me to the mobile site, irrespective of the original domain.

[woobar]

I was wrong, see update.