I realise that it's technically illegal to "look" for work but I've read in other forums and sites that if you just tell customs that you're only on vacation, it won't be a problem. I mean, I can't help it if an employer "decides" to hire me while I'm there, then return to the U.S. so they can apply for a work permit. I hope that this doesnt come off as being nieve but it is very hard to find work on the web. Think about it..if you owned a business would you hire someone just based on a piece of paper.
Actually, if you "just tell customs that you're only on vacation"-aside from it being irrelavent to Customs, since it is Immigration you'e concerned with-it's a serious LIE that could get you deported. When that work permit is applied for, they will want to know when and how you came to be hired. If you lied to Immigration and claimed to only be on vacation, and they find out you applied for a job in that time, your visa could very well be denied along with your rights to visit the UK in future on the visa waiver program.
Lying to Immigration is never a good idea-we have had numerous people here who can attest to that.
Once you have a job interview lined up, you can enter the UK for that and be honest and tell them that's why you're there.
As far as "think about it...would I want to hire someone just based on a piece of paper"...well, no. But I would interview someone based on a piece of paper, as that is what employers do every day. What I would not do is hire someone looking for work illegally after lying to the goverment. Not the sort I would want working for me, I'm afraid.
I hope you get some interviews that you can come over for, though, and wish you luck.