First, the story.
I went from digital to film about a year ago with a Nikon FE and 50mm f/1.4 lens. It served me well for quite a while, but I then started getting interested in rangefinders. I bought a Canonet 28 from a seller on the 'Bay and got addicted. A little while after that, I sold my Nikon in favor of getting something else (was going to go for an FSU camera or two) and a very nice person offered me a Canon P on a trial basis. I am in love.
All that aside, there are pros and cons to almost any type of equipment. If you have one you should have the other depending on your style of shooting. If you like to do street photography yet you also like to do macro work, you're best off getting a good rangefinder and a decent SLR. If you do street photography and landscapes you could get away with only having one or the other. I'm a street photo/candid portrait person and I love my rangefinders for this. The lenses are sharp and easily focused, they are relatively quiet (the Canonet is a very quiet 'click'), and they are much less bulky than the SLR I used to have. I like shooting black and white film and my style of photography is better suited to a rangefinder than an SLR. My personality is as well. I prefer the feel of a rangefinder in my hands to an SLR, even the older, better built ones.
It's all personal preferences and how you shoot. I am yet another one of those people who buys into the philosophy that it isn't your gear that makes you a good photographer, it's your vision. Find what you're comfortable with using and use it. Don't let anyone tell you that one thing is better than another or that one format is better than another. A person who has the most expensive gear and has no vision will still be a bad photographer regardless of what he bought.