Good luck and Bad luck
The simple answer to the beercan is that when you use a premium telephoto (fast constant aperture lens) you should be in the mood to do more serious photography.
Any lens that has a constant f/4 or faster aperture in my book is a premium telephoto lens. The beercan just happens to be a premium lens with an affordable price tag.
Therefore when I shoot with the beercan I'm in a most serious photography mode and the size and weight don't bug me much at all. Take a look at Canons ultra popular 70-200mm f/4 L lens. Great price, sharp, bigger than the beercan.
But photographers use it all the time.
Now on optical quality, the beercan really only has one weakness and that is chromatic aberration- and it shows its dated heritage at that point. The lens is from the mid eighties so for being as old as it is and having only that optical weakness, well, that's pretty good.
Bokeh, macro, sharpness are all very good. It zooms internally so it doesn't change size during that process which makes it a great handling lens (no change in balance during the zooming process, no zoom creep, or anything like that.
The front element does rotate so using polarizers can be a pain, but otherwise, its popular in the A-Mount community for a reason.
It's an acquired taste in a way but when you look at the final images- you'll see what it's all about :). Personally I think the bokeh is as close as you can get to the 135mm STF without spending a fortune on that lens.
Now that I have a real nicer copy than ever, I'm definitely going to be shooting with it much more often.
P.S. if the size absolutely throws you off, take a look at the 70-210mm f/3.5-f/4.5- its sharp as a tack shorter, and has a focus hold button on the side (a feature the beercan doesn't have). You'll give up the internal zoom however.
Ironic Misquote: "Nothing can stop the man with the right mental attitude; nothing can help the man with wrong one."