Do I have enough time? 50 minutes, I probably have to change terminals from domestic to international??
Are you staying with the same carrier or changing airlines? Houston can be walked in that time period, and they also have a minirail from most terminals tho I have found it's not always close. Continental has most of their Euro bound flights grouped at one end of the international terminal but there are moving sidewalks. I am assuming this is one ticket/one reservation and that you will have checked in for both flights in advance, in SFO. If this is 2 reservations, then other advise comes into play.
That is sort of the long way around to A'Dam from SFO. We went from SFO non-stop a few years ago with Lufthansa.
There aresome good food and nice shops at IAH to stretch your legs, and perhaps find something to make you more comfortable on your flight. The duty free shops are run by the same people everywhere- i.e., no great deals, but convenient if you need something last minute. We usually eat enchiladas or tacos at Pappasito's so we don't have to eat airline food and we can go to sleep earlier. This sitewww.ifly.com is very handy. Also for an IAH overview the map here
http://content.united.com/ual/asset/AM_IAH_615x447_1011.jpg may be useful to you.