Palm announced 2k apps on their store and Google recently crossed over 30k. Blackberry has 5k. Ovi maintains about 7k apps.
According to Appshopper there are 199,885 apps approved and 172,662 available on the App Store. (200k will certainly be crossed today March 21st). Due to churn and policy enforcement Apple has removed 27,223 apps from its store over the years.
In the case of Android, policing may not amount to much catalog erosion so the 30k figure is more comparable to the “approved” Apple figure.
With 27th the deadline for inclusion by the April 3rd launch date, the rush to submit new apps for the iPad is on. No doubt, there will be a significant surge in new apps in March. This might lead to a new record of over 25k apps added in one month.
My initial estimate in February for the 200k milestone was by May 1st. I was clearly off by nearly 40 days. If the add rate is maintained at 20k/mo 300k will come around in August although I’m not as confident in this forecast. The rate of app addition seems to be accelerating.