I've tried and generally had disappointing results.
First, since I don't really collect many US coins, I'm not going to spend more than melt on any coin that isn't a Standing Liberty (which I collect) or a Seated or before (where I can sell for a premium). On the off chance I do find an interesting coin type wise, the quality usually isn't there. Unless it is priced right at melt price, or is a rare date/type, when it comes to modern coins it isn't really worth it to get things in any less than XF. I mean, if there is a 1879 Morgan for sale in VG for $30, why not spend the extra $5-10 and get it in XF? Or spend the extra $15-20 and get it in attractive AU or low grade mint state. Obviously, if they had Morgans at $10, I'm going to buy all they have to offer, but buying low grade coins when attractive examples cost just a bit more on eBay or in a coin shop simply doesn't make sense to me. And estate sales are just filled with low grade modern coins.
I'm not going to pay a premium for "fake graded" coins. Sadly a lot of auction houses around here along with many private collectors use strange TPGers (ICG seems to be oddly popular around the auction houses/sales/antique malls around here...) that really doesn't add any resell value to the coin but still adds to the price. Unless it is PCGS/NGC (or occasionally ANACS) I'm not going to pay a premium because the coin is graded. Even though they might be accurate graders, it simply isn't the "brand name" everyone is looking for. I'd rather save a few bucks and simply get the coin in a 2x2.
On the coins I do collect (British coins/Ancients/other European coins) the prices are through the roof due to age/curiosity premium. Sure, your 1797 cartwheel penny is old, but its also in terrible condition and worth about $3, not the $35 you want for it. There have been a few cases of finding interesting die varieties/key dates in estate sales that I've found but overall they are overpriced.
Now, I have found some luck at estate sales and junk box rummaging. I managed to find a 1939 Canadian Dime for 50 cents in a "junk box" today, but the same guy wanted to sell me Maria Theresa Thalers for $45! And $55 for a 1917 Type-1 Standing Liberty which would grade VG at best! And then I've managed to find other things like a 1996 anniversary of decimalization silver proof set (British) for $85 or so a few weeks back (usually sells for about double that online, mintage of only 15,000 sets).
So of course I go to all of the ones I can see, but I end up generally buying very little (or buying some little overpriced coin so as to not waste their time).