Last Sunday I gave my old commute bike the weekly wash, she definitely was feeling very sluggish and squeaky that week.
I cleaned and lubed the chain, replaced the rear derailleur (only a cheap tourney and was needing replacing) and cleaned and lubed the rear free hub, then I noticed something, on my rear brake calliper one of the break blocks was pointing at a funny angle, I reached over to twist it back in position only to find it fall off in my hand!!! (it looked corroded, white but no rust) I'm guessing this was what was making my ride feel sluggish as the brake block was resting on the wheel although I didn't notice any noises.
I'm think I got away with a potentially dangerous brake failure, so will now be checking them before every ride, so might be worth doing the same if you don't already do as you never know!!
BTW my LBS fitted this only 2 months ago, I have lost a lot of faith in them as when I first had it fitted it had worked itself loose only two days later and I had to re-tighten after that it was fine!