I recently updated to Skype 5.8 (had to download it manually, since the update option in Skype always got stuck at "initializing download...").
Then my cut-and-paste (ctrl-C and ctrl-V) in MS excel and word stopped working properly. Formatting was not copied (only text). I tried adjusting advanced settings in word and excel with no luck.
Finally, I found the link below which says the skype add-on (to IE or Chrome) caused the problem. I tried disabling the skype add-on, restarted Firefox and excel and voila! problem solved!
I am disappointed (in Skype and MS) that a simple add-on could break such basic MS functionality. I hope this issue is resolved in the next skype release.
Skype is aware of this issue and has ackwoledged here, among other places:
Please note: I do not respond to requests for help via Private Message.