I'd say there are some services which are definitely safe to disable if you know what you are doing.
I'd say these services are definitely safe to disable for anyone.
Alerter
Error reporting
Messenger
There are many more that are safe to disable if you know what you are doing, but for the complete newbie, the three I mentioned above are probably the onle services safe to disable. The newbie doesn't need to be sending crash data to MS, so Error Reporting is completely pointless and unnecessary and it won't hurt for anyone to have that disabled. The only reason to not disable Error Reporting is if you actually want to send crash data to MS. I don't know why anyone would want to submit information from their PC to MS willingly.