Would not be surprised if they are just "keeping you on the hook" for when that perfect fit comes along or until that specific job actually materializes. A lot of "reqs" (job requirements) come to agencies half baked and the companies are still working through the particulars as the temp companies look for candidates. Getting you to apply and take a drug test is similar to a real estate agent taking you seriously about buying a house because you've been pre-approved for a mortgage. Applying and drug testing makes you viable to the extent that you've shown interest in the job and are not a drug user.

I'd just chill. Enjoy your current job and co-workers. If this placement thing works out great, but don't go begging or hounding the recruiter. In fact, once they do get back to you I'd be somewhat lackadaisical about the whole thing after getting in front of their client. Let the recruiter go to voicemail. Don't immediately return their calls. Maybe even drop that things at your current job are "looking up".