That said, I think your day job needs to be fairly light for this to work. At the time, I was doing light consulting after having sold my first company.
I'm currently working on another little startup idea (http://www.rescuetime.com) but it's been moving a LOT slower, as my day job is something I invest a lot more time and energy into.
Of course, it very much depends on the scope of the problem you are trying to solve. You're never going to build the next salesforce.com as a PT founder. ;-)
You can only be so productive anyway. Just because you spend 8 or 9 hours a day at work doesn't mean you're working the entire time you're there. More like 1/3 of the time is actually spent thinking and working. It's not even that you're being lazy, it's just you burn out if you work too hard and too often.
The strange thing is, nobody who's in a position to hire understands this. And if you do find part-time tech work, you're most likely going to be paid LESS per hour than you would if you were doing the same thing full-time.
so if you have to do your startup with a 40-50hr/wk job, do it as briefly as possible until you can prove to yourself the worth of the idea and then make the jump. and this may sound strange, but get yourself in decent physical shape so that you have more stamina and aren't exhausted after a normal 8-9 hour work day. in my case i had way more energy/focus if i was running/lifting regularly (and frittered around/needed more downtime if i wasn't.)
i'm going full time on my idea at the end of this week and have a lot more momentum because 1) other people will be working on it with me and 2) i will be able to focus 100% and do things like pull all nighters when necessary and basically not have any other constraints in the way of getting things done.
"...Most founders of failed startups don't quit their day jobs, and most founders of successful ones do. If startup failure were a disease, the CDC would be issuing bulletins warning people to avoid day jobs." -- The 18 Mistakes That Kill Startups
I'm onto my second startup. My first one is (just) profitable and my second is showing very promising signs.
I put all the profits back into my businesses, so I work three days a week to pay my personal bills (and temporary business expenses). Fortunately, my job lets me go in whenever I want, which helps me juggle my time.
I think it works pretty well. It's meant I've never had to take any outside investment and yes, working my day job gives me time to reflect and come up with new ideas. It undoubtedly makes me more productive.
I've worked in an office environment where people could easily get away with surfing the web 80% of the time, no big deal.
I've worked from home where Subversion checkins are monitored daily.
No checkin? Well what the heck are you doing from home then? =)
The moral of the story: Working on your startup part-time is a great way to mitigate risk while you build out your first version. However, if you see some traction quit you day-job and start executing relentlessly.
Was your name featured on TechCrunch, or just a URL?
I've tried doing "anonymous" startups under pseudonyms, it's hard to be taken seriously by the likes of TechCrunch, etc.