OK, let's discuss Visa point...
First of all, Visa is not the same as My Space or eBay - even from the TM point of view. All member Banks of Visa have the rights to use Visa name in their promotions - as far as I know members of MySpace or eBay haven't same rights. So, when you are promoting Visa Electron Card of Somewhere Commercial Bank you can absolutely legally open website VisaElectron.TLD without any legal problems - problem goes only to website design, that all member banks have info from Visa Guidelines.
So, nevertheless the fact that Visa is secured brand, there is a good quantity of legal entities that have all rigts to use Visa TM in general and Visa-named domain in concrete.
As for Visa meaning as travel term... there are lots of websites with visa word in it that have no problems with Visa - for example you can see VISA.ORG. Also, there are lots of other domains...
I only want to say, that it seems quite exxagarating to simply copy Visa TM usage rules from website or to say that there are extreme possible TM problems... There aren't definitely.
So, please consider all info and make appraisals with less risk on TM issues...

Thanks.