I'd like to make two contributions. One is very negative (CR is rubbish) and the other is very positive (SSRS is backing store independent and available at no cost).
On a side note, if you mod an answer down then add a comment explaining why you think the answer is wrong or counterproductive, unless someone else already said the same thing. Even then, a simple "as above" would be helpful.
Crystal Reports is rubbish
Crystal Reports is an insult to the development community. Simple dialog resize bugs that would be the work of moments to fix have remained uncorrected over ten years and six major releases, so I really doubt that any attempt is ever made to address the tough stuff. Crystal Reports is profoundly untrustworthy, as this SQL demonstrates.
SELECT COUNT(*) FROM sometable WHERE 1=0
This statement produces a result of one when it should produce zero. This is a repeatable off-by-one error in the heart of the Crystal Reports SQL engine.
The support for CR is equally dismal, having been moved offshore many years ago. If you cough up $200 for a support call, an unintelligible foreigner will misunderstand your question and insult your intelligence until you give up, at which point he will - because you have chosen to give up - declare the call resolved.
If it's really this bad why is it so popular? Great marketing. Management types see glossy adverts promising much, and because CR has been around so long they assume it's all true. When managers lack the technical expertise to make a decision, rather than allow a technical person to make the decision they fall back on precedent and repeat the mistakes of their peers. They also fail to realise that if they want to actually use the web delivery stuff they are up for a server licence. Also, longevity means it's easy to find people with CR experience.
For the details and a good laugh I recommend these links.
Or just type "crystal reports sucks" into Google. For a balanced perspective, also try "crystal reports rocks". Don't worry, this won't take much of your time. There are no positive reviews outside their own marketing hype.
Now for something more positive.
SQL Reports is effectively free
You can install it at no charge as part of SQL Express with Advanced Services. You can also install .NET 2.x which brings with it ADO.NET drivers for major database providers as well as generic OLEDB and ODBC support.
Since SSRS uses ADO.NET, this means you can connect SSRS to anything to which you can connect ADO.NET, ie just about anything.
The terms of the licence applying to SSRS as supplied with SQL Express require it to be deployed and installed as part of SQL Express. They don't have anything to say about where reports get their data.
SQL Express is limited, but the accompanying SSRS has no such limitations. If your data is provided by another database engine you can support as many users as that engine is licensed to support. Don't get me wrong, at work we have dozens of licensed copies of MS SQL Server. I'm just saying that you can use SSRS against the backing store of your choice, without having to find or justify budget for it. What you will be missing is scheduling and subscription support. I speak from experience when I say that it is not profoundly difficult to write a service that fills the gap.
SSRS fulfils every promise that CR makes. Easy to use, good support for user DIY, has a schema abstraction tool conceptually similar to CR BO but which works properly, high performance, schedulable, easy to use, stable, flexible, easy to extend, can be controlled interactively or programmatically. In the 2008 edition they even support rich-formatted flow-based templates (mail merge for form letters).
It is the best reporting solution I have ever seen in twenty years of software development on platforms ranging from mainframes through minis to micros. It ticks every box I can think of and has no profound weakness I can recall.
It does not address problems like heterogeneous data provision, but IMHO these can and should be addressed outside of the report proper. Plenty of data warehousing solutions (such as SSIS) provide tools for solving such problems, and it would be absurd to put a half-assed duplicate capability in the report engine.