By today's standard, mastering is a process that used compression, EQ, and Limiting to clean, tighten, smoothen, fatten, etc. a 2 track mix. Usually, mastering is just a subtle icing on the cake' move. Making sure each song on an album is the same volume and same tonal balance is an important part of mastering. You can easily master in PT, and the waves stuff is used all over professional mastering houses. I have used T-racks, and it sounds good. A lot of people like the renniassance comp/eq with the L1 ultramaximizer. Another popular one is the TC finalizer, and other really expensive tube gear. Monitoring is very very very critical in mastering, and a lot of houses have pairs after pairs of any kind of speaker you can think of. It is worth it to have your mixes professionaly mastered.