Having a community that is comfortable with your office is team is great, but being too friendly can lead to bigger issues or even law suits.
Facebook - This tool can be a great resource for complexes. Being 'friends' with a tenant is really up to each individual, but they should be warned of the negative possibilities. Although you can put restrictions on what people see, it is simply not a good idea.
Personal Conversations - Huge no no! Midy is right in saying that some stories are cute and fun to share, but telling tenants about personal issues can lead to trouble. I have witnessed tenants use personal information against staff, and it is just awful.
Running errands - No one but the office staff should do office tasks. Period.
Flirting - Adults are free to have adult conversations, but not while they are on the clock. If an employee wishes to develop a personal relationship with a tenant they should do so on their own time. This is risky and could end badly, but each case is different.
Remember, the management is responsible for anything that could be considered sexual harassment.
Mindy is correct in saying that residents will share their lives with you, but that doesn't mean you have to share equally. Approach every conversation with caution.