You won't have to worry about creepy men since I won't be there
Nah, you shouldn't have any problems - just keep your wits about you, as you would have to anywhere else.
As for hostels, I always recommend the Astor Hyde Park in London. In Amsterdam, I've stayed at the Flying Pig Downtown, which stays true to its reputation as a party place. The bathrooms aren't atrocious if you stay in a smaller (i.e. 6 person) room. The only thing I didn't like about the place is that it's just about ALL Americans and Canadians staying there, so you don't get much international flavor. That and it's full of people who're too stoned to ever leave the place.
In terms of meeting people in London, besides the hostel, my favorite pub is the French House in Soho. It's so tiny, you're practially forced to talk to everyone around you. No mobile phones or attitudes allowed. It's a young, cruisy scene at the Gardening Club at the Rock Garden Restaurant (Covent Garden) - Tuesday nights are 1.50 drinks! Also tons of nightlife and cool people to meet in the Camden and Shoreditch areas. Earls Court is nice, but I don't know of much going on there offhand.