I doubt it'll effect the tourist trade at all.
This won't be another Tunisia for a few reasons. Firstly Mbarack has the military, media and police firmly on his side. Also the US backs him and Clinton has already come out in support for him.
He might be a military dictator of a fairly oppressive regime with a sketchy human rights issue but he co-operates with the US and the west so will be supported at all costs.
Ben Ali in Tunisia had none of that. He wasn't useful so wasn't backed.
Cairo you would notice something going on - its Tahrir square, the middle of the city. All roads lead there, the Egyptian museum is on that, lots of the main hotels, lots of the diplomatic missions and so on.
Remember it wasn't only Cairo, people were killed in Suez, Alexandria and riots elsewhere. Due to the state media control though its generally not reported at all in Egypt.
Currently in theory Twitter and Facebook are blocked but the government isn't in the same league as China, Saudi and so on in terms of technology. They don't/can't do backbone blocking and rely on telling ISPs to block it.
Skype has been "illegal" and "blocked" for a year but still mostly works even on mobiles. They have the will to control the internet but not the technological ability.
Egyptian culture is quite different as well - i doubt they've got the balls for extended protests to bring about change.
Most likely it'll all calm down now as they're getting bored already. Expect a massive government and police crackdown before the sham presidential elections later in the year though. By then they'll probably have more ability to block internet traffic, mobile phones and so on.
Ultimately its in the wests interest that Mbarack wins anyway so they'll back him no-matter what.
They really don't want democracy as that would guarantee a less favourable leader there.
I really can't see it affecting a tourist at all, especially in May. Sinai i doubt you'd notice anything going on at all.