I got a similar letter a couple of weeks ago and ignored it. I just bought two domains recently and completed the update by putting me in for each contact back in November?, I think.
You might wish to read what the TOS says about posting e-mails. Big no-no around here. Paraphrase the content.
You can safely ignore it though, you only have to/are supposed to take action if the whois info is incorrect.
...but even if it is, I doubt it will have any consequences.