re all the other 'not me's here:

I had no problem for about two months of almost daily use (train commute), then I started getting my HTTP browser pages redirected to a tethering upsell page. HTTPS still worked, as did e.g. imap, dropbox, skype, etc, but I haven't personally played with it enough to find out if it seems to just be the user agent. The HTTPS-everywhere extension will probably help significantly with this, if you're looking to evade, if that's all they're doing.