I shoot most often with an Aria and the 45mm Tessar. I got into Contax because of this lens... at the time, Nikon had yet to release their 45mm, Pentax was being idiotic about making their 45mm pancake widely available, and Olympus had discontinued theirs, so I went with the Aria and the Tessar.
The idea was to have a SLR I could just wander about and take pictures with, and not worry about weight. I'm not into rangefinders or P&Ses (I love Depth of Field preview too much), so a small SLR with a tiny lens was the perfect compromise.
The results are phenomenal: in the right light, the tonality and subtlety of color are amazing, I learned the value of good bokeh, and yes, it's tack sharp. I will second the sentiment expressed by someone else that it can be a bit too contrasty in glaring bright light, tho... images can look overexposed under the wrong circumstances.
All in all, a great performer. My particular ex&le had awful build quality, tho. It's already got a cleaning mark, and the focus action is too stiff, causing the lens helical to come loose, to the barrel of the lens rotates a small amount when you focus it, very disconcerting. I'm sending it in for another repair, but I may just get another. I've been told that poorly made lenses of this type are very rare... just got (un)lucky, I guess.
Flaws and all, I use it more often than my exquisite 28mm f/2.8 and so-so 80-200 f/4. (This was also a turkey in build quality... it focuses past infinity to unsharpness, the filter threads unscrewed off the barrel along with the polarizer, and the zoom action is way too stiff. Image quality is nothing short of awesome, tho.)
I like the slightly wider "normal" aspect of the 45mm vs. a 50mm, the Tessar provides a distinctive "look" that's neither Planar nor Distagon, and I really like it's tiny size... the 50mm 1.7 and 1.4 may offer slightly better image quality, but they are big and bulky.
So, I say, "Go for it!" Warts and all, I'm not unhappy with mine as a daily shooter.
Matt Gabriel