Hi, Kathy,
Adding my two cents (or tuppence) as I frequently do -
The only time I've left a gift for a B&B owner was on Skye, when the owner offered to do our wash, as the laundrette in Broadford was closed (Not that the machines ever worked, anyway - one year we did the wash, only to find out that the dryers were broken. We had to take a bag of sopping wet wash to Portree to use the dryers there.). Anyway, this very nice lady did our laundry for us, at no charge.
As we were coming back across Skye from Harris, we decided to bring her a small token of our appreciation. A couple of boxes of Cadbury's Roses filled the bill. We bought them at the Co-op in Broadford; if we'd bought them in Portree or Stornoway, we would definitely have finished them ourselves before we got back to Broadford! :)
As far as leaving a tip for housekeeping in a hotel, I usually leave a pound or two if I'm staying more than one night, but not on the last night, as I won't be coming back.
As far as restaurants go, a 10% tip seems to be the general consensus here. I know that tipping in a pub is not generally done, but especially if you're going to be in the pub for a while, it wouldn't be amiss to give your bartender/publican a pound or so, or tell him or her to keep the change if you have a small amount coming back. For reference, see the patrons at the Queen Vic on EastEnders.
As far as taxis go, I know that most guidebooks say to just round up to the next pound, but give me a break! These men and women are working hard for their money - think about how much you'd enjoy driving all day in Glasgow or Edinburgh. Round up, then add a pound or two. Just think of it as contributing to the Scottish economy.
Happy travels, and happy tipping!
Mike (Auchterless)