Working for company but now consultant

I currently work with Company X who has numerous business dealings with Consultant Company Y. The IT dept is being outsourced (namely my position – part help desk part sys admin). Consulting Company Y is willing to hire me and provide me with tools and resources to get the job done at Company X who would then be my client. Does anyone have a bad experience they want to share? I want to make sure I have covered all bases. Thanks in advance for any replies.