In reply to BnB:
My experience differs.
I regularly go camping with my parents in May for a week. Very early may midges are normally there but more of a oh look there's a single midge biting me type experience. By mid may West Coast Scotland is normally pretty bad for Midges, enough so that you wouldn't want to be eating outside in the evening on a campsite. This is based on camping in Skye, NW highlands, Lochaber and Arran. OK sure they aren't as horrific as they would be in mid august when you can literally see them liberally spread throughout the air as you drive along (in some locations) but still they are typically quite annoying.
That said Midges don't like wind or sun, as long as it's sunny (and not a few hours from sunrise / sunset) or windy (above 5mph) you won't get bothered too much by them. Scotland is a windy place. I've camped for a week in mid June in the NW highlands and hardly seen a midge.
If you aren't camping and you don't intend to stay still for long periods in one place then I wouldn't think they'll bother you too much most of the time, but occasionally they will probably just pretty bad. Equally if you are climbing and you are in the sun or the wind they won't be too much trouble either.
If you are camping after mid may your best chance of staying midge free is to camp as close to the sea as possible (preferably without any bog / marsh between you and the sea). Generally I rarely plan to cook on the campsite in the midge months, going to the pub is a much more pleasant experience.
Post edited at 09:14