1. How to consume a web service in Android? Any pointers or link to simple tutorials would be useful.
At the easiest, web services can be called using the HttpURLConnection class. If that's available (check the Java API implemented by Android), then you can call web services.
2. Since there are performance issues associated with web services - what special care needs to be taken when using them in Android applications?[/qupte]
What kind of performance issues are talking about? How would those affect the client?
By performance I meant speed; are there ways to improve the response times?
Nothing particular to Android. Obviously, there are many many ways of improving performance of Web services and their consumption, but those are mostly Web service-related issues (e.g., using If-Modified-Since).
You might also consider using the Apache HttpClient API, available in Android. I tend to use that instead of URLConnection.