Just a quick preface: I don't mind having advertisements displayed to the few people who read my single posts when not logged in to WordPress. I pay for the Custom CSS upgrade on a few of my blogs and at about £9 a year per blog I think the wordpress.com platform is pretty amazing. I don't really care enough about ads to pay for the No-Ads upgrade even though it isn't very expensive.
However when ads do show up I'd quite like to be able to style them so they're not so in-your face and fit with the rest of my site. I very much doubt this is against the terms of service. The problem is that the ads are inconsistently styled to begin with so if I try to set some of the text a little smaller and then view a different ad on a different page it will be too small to be legible (something I'd like to avoid doing because then it does look like I am attempting to sneak around the TOS). I'm not sure if this is could be fixed on the WordPress end or if the ads arrive wholesale like this from Google themselves, has anyone ever looked into this at all?
Also I distinctly remember the ads being described on one of the support pages as "text" and since looking into it I've noticed that I get a few large-ish image advertisements (or flash files disguised as images) cropping up now and again which is a little bit cheeky.