When you fill an online form, you're basically saying "Here's my details - who thinks that looking at these I'll make a good customer?".

Usually the forms are syndicated out to different lenders, who then often reply directly to you with their offer, so you can pick and choose.

The warning I'd give is not so much about giving your details online - as much as be aware that if vendors contact you, they will have some of their smoothest-talking salespeople do it.

So ensure you don;t make any snap decisions over the phone, and do look to consider all offers in context.

Also ask about various associated fees, such as early repayment and exit fees, in case you want to look to move to another provider a few years down the line.

If you're in the UK, you could use a reputable broker, such as here:
Mortgages - Compare Mortgage Deals for homeowners and first time buyers

where they are accountable to the FSA, FISA, etc.

Great advice Brian. I know I was trying to figure out what the going rate was one day. I don't know what button I pushed, but for several months I got regular calls from people wanting us to refinance through them. I just wanted to know the interest rate - not refinance.

Thanks for that link Brian Im sure it will come in usefull!