1. The Bell hop that brings the bags to your room.
Generally don't use a bell hop. When I'm staying in a hotel, I usually only have my laptop bag & 1 case, so I can perfectly manage getting them to my room thankyouverymuch. However, on the odd occasion when I've used their services, it's generally $1/$2 per bag.
2. Hotel Doormen.
I only tip them if they provide an extra service, such as hailing a taxi, and then only $1 or $2.
3. Maids in hotel roomsÉ and how should this tip be leftÉ with a note?
I've rarely left a tip for the maid - unless they've done an outstanding job or I've been particularly messy

4. A gentlemenÕs barber.
For me this all depends on the relationship you have with your barber. When I'm in Napa, I have a regular place I use and usually tip the barber $3 or so. Back home, my local barber charges £7 to cut my hair and I've been going to him for a while now, so if I'm feeling flush I'll round it up to a tenner. Both home & away though, if I've not been there a few times before, I won't tip.
Cheers
Michael