Not a side project, per say, but I answered questions on my local Linux User Group almost daily. After applying for a job and not hearing back, I got a request to come in for an interview weeks afterwards. Long story short, the boss told me he saw my responses on the mailing list and it turns out I knew more than the RHCEs and CCNAs walking into his interviews.

That landed me my first job ever in IT as a Junior NetEng and eventually a Linux SysAd.