100 days is a nice round number, but it is too early for a critical review. But good opportunity for some thoughts. I agree with Alexander, more patience. This site has many high rep users with academic background near or in biology when you look up the users page. I like the level of questions between popular science, textbook and research-related. Having the opportunity to get answers on research-questions would be fine, but this is very hard for experimental branches. Look on physics.se, there are nearly zero questions on experimental research questions or tricks. This type of questions are often too localized and tricky so that you cannot promote a coherently interested community with it. Even theophys.se (despite many phd and profs post there) has a hard time to produce enough good questions. This is more caused by the nature and scientifc questions of this discipline better fitting a discussion than a Q&A format than some mismanagment/moderation or failed area51 process. Mathoverflow or cstheory.se work because a single smart mathmetician or programmer can understand and solve a much broader spectrum of problems and questions in that branch (similar language and methods in many math. subfields), while experimental/natural sciences disciplines need a lot expertise and experience in distinct subfields.
The chemistry.SE is going to start soon, also over 50% academic commiters, which looks very promising for such a much less popular scientific branch than physics or biology (I dont know a good chemistry blog :) ) So this will add additional expertise and questions to biology.se and physics.se. I havent seen many user from physics.se here, but this will probably be different for chemistry, which has stronger overlap with biology.
There is always the problem of finding a common denominator between popular science and research level. And it is known now, that research-level questions are better put to a new proposal (tcs.se or theophys.se) when you have attracted enough students and professionals on student-level sites like physics.se or stackoverflow. Why not make a theoreticalbiology.se proposal when the time has come? Patience, this site looks very promising and computationalscience.se, chemistry.se, physics.se will probably create quite some synergy effects in near future.
Something I'm unsure about is if questions on experimental methodology (like NMR, scanning probe techniques, microscopy, there was recently a question) should be migrated to physics/chemistry.se. These questions are often tricky, but also these experimental measurement methods are often strongly adapted to specific experimental questions in a scientific branch. Most physicists (I am one) dont have background in these highly tricky methods, it's more likely a physicist working in biological research and surfing this site or a good biologist with experimental experience can give you a answer on biology.se. You wouldn't ask about biomechanics of a cheetah on physics.se, although it is plain physics, only biologist are interested and teached in this stuff. Maybe somthing that should be discussed in another meta thread, but belongs to the future and scope of this site, so seems good opportunity to mention it here.
The cognitivesciences.se is currently imploding (a lot of meta discussion, very bad stats and a failed area51 process). So trying to answer some interesting neurobiology questions here rather then migrating them there is also something I want to point to. Neuroscience/-biology is a interesting topic. But gathering experts for these type of questions will IMHO only work with a high quality biology.se and theobio.se site. SE fails to attract user with serious background in humanities (psychology, philosophy) as a site for mainly STEM and Programming students & professionals. This is no surprising thing looking at what proposals work and not work on SE.