I have one of these beasts. I bought it off a retired guy who couldn't be bothered to use it anymore.
It really is a massive camera, built like a tank. It's a bit of an ergonomic nightmare to use, IMHO, but it produces great photos.
The 105mm F2.4 lens is arguably the best in the Takumar series. I have seen some really incredible photos taken with that lens. It has great color rendition and nice bokeh ... it's also not an expensive lens (I bought mine 2nd hand for $100 USD) so it's a great value for what you get.
Watch out for the mirror slap! You've probably already read or heard about it. Ka-POW! There's a lot of kinetic energy every time that mirror flaps up and down. For me, I try to stick to the rule of not using a shutter speed lower than the focal length if I'm going hand-held. i.e. with the 105mm, I wouldn't shoot in at an aperture where the light meter was giving me less than 1/125 to work with. Although, if I was REALLY steady, I might try 1/60th.
Conversely, I've taken multi-second exposures at night, resting the Pentax against a park bench for support -- and they turned out beautifully.
BTW I have a few of my 67 shots here, if you're curious:
http://www.flickr.com/photos/bobby_novatron/sets/72157623803689122/
Good luck with your new purchase!