4 what non-subscribers see on a getitem link
1. Google scholar is free; MathSciNet requires a subscription. In practice the usual effect of this is that one needs to access MathSciNet via a university IP address rather than one's home address. But it also means that one can't provide web pointers to MathSciNet searches or reviews and expect them to be usable by people who are not themselves professional mathematicians; one can only provide links it is possible to link to bibliographic entries for individual articles and but non-subscribers are not shown the review text, only if one knows to use the "make link" buttonbibliographic data.

2. MathSciNet covers essentially all mathematics journals; Google scholar covers only what it can find online. On the other hand, Google scholar covers unpublished preprints and some published mathematical material in related disciplines (e.g. theoretical computer science conferences) that is not as comprehensively reviewed in MathSciNet.

3. MathSciNet is indexed only by title and abstract/review text; Google scholar is indexed by the full text of the article.

4. Some articles in MathSciNet have a review written by a knowledgeable reviewer, that puts the article into context better than the authors did. (On the other hand, many MathSciNet entries merely repeat the authors' abstract.)

5. MathSciNet has much more reliable publication data than Google scholar: its BibTeX is generally usable as-is, it properly collects papers by the same author and distinguishes papers by different authors, and it doesn't have duplicate entries for the same paper. However, Google scholar generally has better citation data than MathSciNet: although MathSciNet lists the papers that cite a given paper, the ones that it lists are generally a small subset of the ones Google scholar finds.

6. Google scholar will provide links to as many different online copies of a paper as it can find (e.g. preprints from the author's home page); MathSciNet will only provide one link, to the official published copy, and will do so only for a subset of the journals it covers.

3 added 201 characters in body
1. Google scholar is free; MathSciNet requires a subscription. In practice the usual effect of this is that one needs to access MathSciNet via a university IP address rather than one's home address. But it also means that one can't provide web pointers to MathSciNet searches or reviews and expect them to be usable by people who are not themselves professional mathematicians; one can only provide links to bibliographic entries for individual articles and only if one knows to use the "make link" button.

2. MathSciNet covers essentially all mathematics journals; Google scholar covers only what it can find online. On the other hand, Google scholar covers unpublished preprints and some published mathematical material in related disciplines (e.g. theoretical computer science conferences) that is not as comprehensively reviewed in MathSciNet.

3. MathSciNet is indexed only by title and abstract/review text; Google scholar is indexed by the full text of the article.

4. Some articles in MathSciNet have a review written by a knowledgeable reviewer, that puts the article into context better than the authors did. (On the other hand, many MathSciNet entries merely repeat the authors' abstract.)

5. MathSciNet has much more reliable publication data than Google scholar: its BibTeX is generally usable as-is, it properly collects papers by the same author and distinguishes papers by different authors, and it doesn't have duplicate entries for the same paper. However, Google scholar generally has better citation data than MathSciNet: although MathSciNet lists the papers that cite a given paper, the ones that it lists are generally a small subset of the ones Google scholar finds.

6. Google scholar will provide links to as many different online copies of a paper as it can find (e.g. preprints from the author's home page); MathSciNet will only provide one link, to the official published copy, and will do so only for a subset of the journals it covers.