Most of us who see many of these terms in print more often than we hear them on radio or TV are more than likely to mispronounce them and make fools of ourselves in the process.
- C#: like "see sharp"
- GNU: guh-noo'
- Linux: Lee'-nooks or Lihn'-ucks
- MySQL: My-ess-cue-ell' (NOT my sequel)
- PostgreSQL: Pohst'-grehs-cue-ell'
- vi: vee-eye' (NOT sihks)
And most surprisingly...
- Netscape: Moh-zihl'-lah (source: http://packages.debian.org/stable/web/netscape-base-473.html) which is as probable as oiseau pronounced "wah-zoh'"
/msg me with more, or add your own writeup. Note that I reserve the right to absorb writeups (maintaining attribution) and have them nuked, so as to keep this from becoming too GTKYNish.