Here's a timeline of my interview process which took roughly 4 weeks:
1) Phone interview with recruiter
2) Google Hangout with 3 Thumbtackers, including Hiring Manager
3) On site interview at Thumbtack SF with 4 Thumbtackers + 30 minute exercise
4) Call with Director of HR
After the on site interview, I had other offers on the table. I asked the recruiter if the team had any reservations or concerns about me taking on this role - there were none. However, they wanted to interview more candidates who were still early in the pipeline. They couldn't move quickly enough due to scheduling issues with Thumbtackers who were on vacation.
Some feedback I'd give Thumbtack - if you have a quality candidate, move forward with an offer. You'll lose great candidates if you want to try to find the next best thing. I accepted an offer at another company due to this situation.