The OS X 10.10.1 update is recommended for all Yosemite users. It improves the stability and compatibility of your Mac. This update:
- Improves Wi-Fi reliability
- Improves reliability when connecting to a Microsoft Exchange Server
- Improves reliability sending Mail messages when using certain email service providers
- Improves reliability when connecting to remote computers using Back to My Mac.
So there's your Wi-Fi fix.